butt in
verb
- to interfere in other people's affairs
Wiktionary
verb
- To join a conversation or situation in which one is not welcome or invited; to interject (connotes a rude or discourteous interruption).
“Hey, this is none of your business; don’t butt in!”
“Forgive me for butting in.”
- To join a queue not at the end, but in the middle, in violation of etiquette.