Is it a guy thing or is it just me?

It's a friendly game. It's at noon in the scorching sun. It's just a 4-on-4 game. It's a mini pitch. There's nothing official whatsoever.

Why would you lecture your own cohort for slacking off in a silly football game?
Why would you tease someone, nonstop, that he has two left legs because his shots are far away from being on target?
Why would you moan about injury every time you missed a goal when you had a golden chance?
Why would you even say "I want us to win" when nobody is even keeping track of the score?

Is it the guys' obsessions about victory that I just don't have?

Frankly, though, I think you should be more mature.