Colleague has sent me a dick pic

Yes, that's true and that would be more complicated to get to the bottom of.
But sending someone a photo of an erection? It's not really a grey area, is it.

Asking someone on a date or complimenting someone at work could well be about perceptions, I agree. Sending an unsolicited explicit picture is not a "grey area" it is quite clearly something that would be extremely unwelcome to most people and highly unprofessional.

Report to HR and the police.

Open a complaint in writing HR immediately saying you don't want to mention the person but this is what happened.

This gives you scope later to report him fully, if his behaviour gets worse or you find out he's done it to other colleagues, with a contemporaneous complaint at the time that gives you credibility.

Just in case he does it again or does something else dodgy.

Totally inappropriate, you shouldn't have to deal with this from work colleagues. Take it to HR, nobody else needs to know, he's out of order and you haven't done anything wrong.

Do not do this. You are making a joke of the incident and not treating it seriously. What happens when he sends the 'unclothed' version so you 'don't need a magnifying glass'.

Send the message you mean- 'Please do not contact me again. This is offensive and unprofessional and in no way solicited by me.'

If a guy approaches a girl at work and asks her if she wants to go out for a drink, and she feels totally appalled by the question and reports it to HR as harrassment, then it would also kick off a disciplinary procedure. This whole matter is all about perceptions. If you feel victimised then you have to be taken seriously.

I agree.

I can’t believe anyone would believe sending to everyone or speaking to him alone are good ideas. It could have consequences for OPs safety and her career.

At the moment, OP has done nothing wrong. Keep it that way by remaining professional and reporting to HR.

Fucking hell @Treestumpp sending a pic of your hard on to someone who hasn't asked for one isn't a 'minefield'.

I wouldn't reply at all, just block. Go to Hr or your boss on Monday.

Please don't even consider leaving unless you absolutely want to, this man does not get to alter the course of your life. I also hope that you don't feel the need to avoid work drinks. Get angry and feel the injustice of it. Honestly op I am so angry on your behalf.

If you start to feel that you are being made out to be a trouble maker then just let your side of the story out. I assume that your workplace wouldn't look kindly on his behaviour. To be honest he has more to lose than you, you hold the cards.

but instead had asked her for a drink.

How is that comparable to a photo of a close up of an erection under shorts?

You screenshot and report to HR and make sure you don't delete it. If anyone dares say anything to you just say 'he sent me a picture of himself with an erection and I didn't ask for it, how disgusting is that?' and that's it. You are leaving anyway so there's no issue there. Again, make sure you don't delete the photo, even if HR request you to. He can't lie then can he?
How rank though 😡

You can give it the ACAS all you want, the employer will deal with it and its not clear what would happen. Ultimately what does the OP want to happen??

Plus its by no means a straight forward case. Had it been out of the blue to Doris from accounts then the bloke may have come a cropper but this is much more complex. There had been some messaging, construed possibly as flirting by the chap. Indeed the OP says she was kinda interested in him before this happened. We werent there so we dont know if this was the start of a non work relationship or not. What Im trying to say is its about much more than just the picture. Lets assume he hadnt sent it but instead had asked her for a drink. Is that innocent or could that be harrassment? What if he'd paid her a compliment? That can be harrassment. It's a minefield.

The OP can do whatever she wants but really, you dont just tell HR and thats the end of it. You need to be aware of the can of worms being opened.

I would actually grab the bull by the horns, as it were.

I would reply and say something along the lines of "why have you sent me what is, in effect, a dick pic? Maybe you didn't realise this is how it comes across, but this is what it is. If I decided to forward it to HR and complain about sexual harassment, you could find yourself in deep shit. I really recommend you check your photos before sending them to colleagues."

Then block.

If you don't want to report then fire a warning shot.

I would reply with "I don't know why you would send me this photo, it's incredibly inappropriate and misjudged"
Give him a chance to apologise and then make it clear your friendship will be purely professional and work based from now on.
Then just move on.

I'd straight out call him out on it, no banter about it.

"Honest question Steve, why do blokes send dick pics to women they are talking to? Do you think we find it sexy and attractive? Because we don't, we find it uncomfortable and awkward, and it just proves that you don't respect women and you obviously don't have any respect for me"

@BirthdayRainbow OP has indicated she doesn't want to make things awkward so I was suggesting accordingly. It's not what I'd do. I'd tell him I'd be reporting to his manager/HR and block him. But that is definitely going to be divisive.

This.

Don't say this. It isn't a strong response.

I wouldn't call you an idiot, but responding to the sender is not how to deal with harassment in the workplace.
We're not talking about shutting down a bit of flirting over the coffee machine.

I'd just reply and say - 'listen, I don't want to make things awkward given we work together, but this isn't OK. Don't do this again. It's unprofessional. Thanks.' Then block.

Why do you think he should get a second chance (if indeed this is the first time).
Are you suggesting he might not have been aware of what he was doing and that it was sexual harassment?

Why would i be an idiot? That text is telling him straight that im not interested and its not all that. The thought of someone laughing and insulting his dick pic is going to stop him sending future ones. If i sent a pic of my breast in a bikini and got the reply of Ewwww saggy tits it would make me think twice.

Having a different approach to things certainly doesnt make me an idiot.

It's quite clear.
From acas

To be sexual harassment, the unwanted behaviour must have either:

• violated someone's dignity, whether it was intended or not
• created an intimidating, hostile, degrading, humiliating or offensive environment for them, whether it was intended or not

You arent responsible for jeopardising his career.

He is responsible for the dick pic, you are in control of your reaction. Dont feel guilty for his behaviour.

If you're worried about being mean to the poor sad old bloke who totally overstepped and thrust his cocknin your face, go to HR and tell them you're upset and can they talk to him about it. He will say its a mistake, they will let him off and he can go on to bother the next poor woman.