Wiktionary
butt in
vb. 1 (context idiomatic English) To join a conversation or situation in which one is not welcome or invited; to interject (connotes a rude or discourteous interruption). 2 (context transitive English) to join a queue not at the end, but in the middle
WordNet
Usage examples of "butt in".
We had a hell of a time to get in and the night we got there, just before dark, and saw it, there was a deep pool and a long straight stretch and the water so cold you couldn't keep your hand in it and I threw a cigarette butt in and a big trout hit it and they kept snapping it up and spitting it out as it floated until it went to pieces.