The difference between a gym bunny and someone who just works out a lot is the latter exercises to be able to do physical stuff like move heavy objects on a regular basis, whereas the gym bunny does it exclusively for visual reasons and probably couldn't do anything with those perfectly toned muscles if they had to.
1. They're amazingly well-sculpted but still seem unable to do anything involving physical labor.
2. Often talk with friends about how much time they spend at the gym and overtly cut meetings and social events short because they have to get to the gym.
3. Act as if their physical fitness by itself makes them better than others.