1. interrupt or intrude on somebody or something
I don't need you butting in!
If you interrupt someone else's conversation or intrude on a situation that does not concern you, then you 'butt in.' Unless there is an urgent reason for doing so, it is considered highly rude. You can mitigate the negative aspect of it by asking permission first. For example: 'Excuse me, do you mind if I butt in?' or 'Sorry for butting in, but...' This expression is common in both a social and professional context.