I think that's enough for me

👍🏼

When would someone say this? When they're refusing another drink? When they can't endure something any longer? When they've already taken too much of something or from someone?

Both of them. Usually people say it about drink or meal. Also, it has a wide using when we're talking about work. (I'm tired, that's enough for me) And, of course, when the person doesn't want to hear boring talks or does't want to take part in them.

Но когда говорим о работе или скучных, отнимающих время, разговорах - очень распространено - "С меня хватит!", "С меня достаточно".