The guy at the gym projecting the boulder problem next to you, the guy you’ve never seen before: 9 times out of 10 times he’s a really nice guy.
A greeting or a friendly comment is enough to break the ice.
Best case: he has an interesting story, or perspective you can learn from. He becomes a great friend.
Worst case: he’s the jerk you said “hi” to once.
It’s worth being the one who goes first. The odds are in your favor.