There's two kinds of situations in my perspective. There's a
gunner move and a
gunner mentality. A gunner move is what
@getfat mentions about the Sub-I straight up lying for gain at someone else's expense. Gunner mentality can actually be more annoying because it's harder to call out and because it's almost subconsciously ingrained in all of us. I would argue 95% of medical students/residents have had a gunner mentality (including myself at times) at some point which is not surprising because it's something I think medical schools select for.
Examples of Gunner Mentality:
M1/M2:
A-Making others feel bad for studying (while they study themselves)
B-Humble bragging about their grades when in reality this is the second time they've seen this material (i.e. masters, SMP, etc) which makes other students feel like they're dumb.
Controversial but I don't think "hoarding" a resource if gunner mentality in the digital age. Obviously this is a competition and if you've found something useful online, you don't owe your classmates anything. Also, I don't think lying that you're doing something else when you're really studying is a big problem unless you're super flamboyant about it. Too many people will judge you for studying (i.e. gunner mentality). Unless you tell someone they don't need to study or you're bailing on a commitment you made with that person, I don't think it's anyone's business to know how much or often you're studying. They should study how much they think they need to.
M3/M4:
A-Feigning enthusiasm for something to try to earn favor of the attending. Rinse and repeat each rotation. It's one thing to say I'm interested in Dermatology, but I want to learn all of this as opposed to saying I love IM and want to do it simply to maximize any subjectivism points.
B-Mind-games commonly employed when designating who gets to see which patient. Oftentimes someone who wants to shine will look at the board and try to get a sense of which patient will be best for them to take and gun for those while giving their peers scut. This is avoided by just deciding on a system at the beginning and sticking to it out of fairness.
The worse part about gunner mentality is, like I said, it's difficulty to call out. For M3/4 Example B, that sort of a thing is really damaging but you can't really tell anyone about it because you're going to be seen as the issue if you make a stink about it and sometimes people just say too bad, that's part of the game and don't care about it.