1. To begin in very fun, exciting, or attention-grabbing way. Live performances from some of the biggest names in the music industry ensure that the festival will start off with a bang. The film starts with a bang, thrusting the audience into the middle of a high-speed car chase within the opening moments.

2. To do something very fun, exciting, or attention-grabbing way to mark the beginning of something. In this usage, a noun or pronoun is used between "start" and "with." Let's all do some Jell-O shots and start this party off with a bang! The committee wanted a huge fireworks display so they could start the graduation ceremony with a literal bang.