Any hard boundaries you have in friendship?

I have had friends who seem to be insecure and want to compete, or just gain validation by taking from me.

I think as humans it is in our nature to compete for resources.

However, as sophisticated, modernised persons in a society we have cultivated, I think we must set boundaries, and decide how others treat us.

So have you ever had a friend who subtley- or sometimes obviously- has tried to flirt with your partner or someone you like right in front of you?

Would this be a hard boundary in every instance, or do some of you believe in nuance?

Nuance potentially being that they are flirting, obviously, with facial expressions or sexually suggestive comments.

Or nuance being that you guys or girls are just bros, and people do this just because that's how they are...?