Billy big Bollocks 

Someone who exhibits signs of being braver or more confident than they actually are

Look at Billy big Bollocks over there, trying to pick a fight with that big bloke.

Billy big Bollocks by Morriarty! May 12, 2011

Billy Big Bollocks 

1. An individual who thinks they are better than everybody else. Essentially, a prick.
2. An individual who suddenly becomes braver than they normally are. Essentially, a pussy

Billy: Oh hey, do you fancy doing a skydive for charity?
Tilly: Ooh, look at Billy Big Bollocks.

Billy Big Bollocks by Pet Wussy July 2, 2020