Actually, it is...
Not that the guy I'm guarding is going for a 360 lefty slam, but you gotta cut off the showboaters, the leapers, the "tough guys", and pester the shooters, or you give them confidence and they just hand it to you. Basketball 3 on 3 is just as serious as 5 on 5 high school and junior college, but lots more screwy stuff and some long lean players also.
It's a question of pride. Much more so than tennis. In tennis, the victor can often go to the practiced and experienced. In Bball, it's a given EVERYONE gets the practice and experience, and you're testing your manhood out there, if you choose to step onto the court. All that trash talk, all the posing, all the behind the back and stepback blocking stuff, you gotta step up and force them to take you seriously.
Gotta admit, I was quite the failure in KezarStadium's 3 on 3 league, but I got to guard some future NBA players, and quite a few college players who didn't make the pros.