Big puppy
A real big dog, a bloke who definitely hits the gym (among other things). Can also be used to describe anything that is abnormally large in comparison to it's average height (e.g. a Barge could be called a "Big Puppy").
When that one national powerlifter in your rowing team takes his shirt off for the boys:
"Oooh he's a big puppy boys!"
"Oooh he's a big puppy boys!"