There is no conclusive list of red flags. A red flag is a feeling you get, not a behaviour he displays. This is really important.
So, there are behaviours that are universally unacceptable, which will be listed if you search for 'dating red flags'. Things like any kind of abuse, keeping tabs on you, disrespecting boundaries etc. But that's not conclusive.
The question you're asking is a bit like 'Is this a turn on?': it's not up to anybody but you to say if something turns you on or not. And nobody can tell you what gives you the 'red flag' feeling either.
The feeling that made you ask 'Is this a red flag?' is the red flag feeling. When you meet a compatible partner, the words 'red flag' won't cross your mind. So as soon as you wonder if a bloke has exhibited a red flag behaviour, get rid of him.
The only time you question this is if you find a pattern where you've dated 20 men, and all of them appear to be exhibiting the same red flag behaviour. You get rid of them, all the same, and you make sure it's not an issue that you have that you want to sort out. For example, if you find that they all make remarks that make you distrust them, you might want to check out if you have trouble trusting, in general. But even then, you'd want to find someone who didn't give you that feeling, so it's the same result anyway: bin anyone who gives you the red flag feeling.