When one bites on or, includes themselves, to an idea or plan when they were not invited or asked to join, usually when intentionally uninvited.
When a club/party/event is going to be off the chain, when anything is fucking sweet. Can also be used interchangably with jump off as chomp off
Once again Alan is chomping in on our plan, when will that kid learn he is a fucking clown.
This place is CHOMPING! This is the chomp off