To feel they should invite me?

[Dreamonastar]

I started a new job recently and there's a lunchtime tradition on a Monday where people go to a local cafe for lunch.

I haven't been invited - AIBU to think it's a bit mean to overlook me?

I'm not a "dropping hints" kind of person I'm afraid - I would just ask them outright (not in a pissy or aggressive way).
"Hey is everyone invited to the cafe for lunch? Can I come? Budge up then!"
But that's just me

What are they like to work with otherwise OP? Are they friendly towards you?

I think it's shows a staggering lack of self awareness not to mention it to you.

They've been quite nice but maybe it's just they have worked there a while?

No, a warm, friendly welcoming work place would tell you when you started about various traditions they have and make a point of trying to include you in them. Whether they mean to or not, they are excluding you.

What do they say to you when they come back?

They don't say anything, really!

Well I think it's bloody rude of them, sorry. How did you even come to find out about the cafe anyway? Surely someone must have mentioned it to you. Why didn't they follow it up by asking you to join them?

Are they all men off to the local curry house or something? That's bizarre.