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butt in (on someone or something)
to interrupt someone or something. Pardon me for butting in on your conversation, but this is important. John butted in on Tom and Jane to tell them that the mail had come.
to interrupt Sorry to butt in on you like this, but there's an important call.
Interfere, interrupt, intrude. For example, Mom is always butting in on our conversations, or It's against the law for employers to butt in on personal matters. This term alludes to the thrusting of an animal with its horns. [Slang; 1890s]
To intrude upon or interrupt someone or something: You're always butting in my conversations, and I wish you'd stop. I can't believe that you butted in on that meeting! We were having a good talk until you butt in.