I didn't say that the Mars bar eater is abusive. I said it's important to heed your own red flags, regardless of what the world tells you is or isn't a 'red flag' behaviour.
There are a set of behaviours that are abusive, absolutely. But you can put your own red flags anywhere you please. A worthy partner will respect them and be supportive of you, even if they're in unusual places. 'I'd like to understand more about this Mars bar thing, can we talk about it?', for example, rather than 'Don't be stupid, it's just a Mars bar.'
Recognising that you can have your own set of red flags that's different to everybody else's is to recognise your autonomy, your own personal boundaries, and the fact that, other than laws, there is no external set of rules for us to refer to, so we have to go on what we feel.
A weird phobia about Mars bars is not a red flag
I agree. Your feeling about your partners response to your phobia is.
You don't understand what red flags are, so pleaase stop using this term. You run the risk of confusing people at a vulnerable time in their lives.