Why do I get angry when I'm hot?

okay so I'm halfway done mowing my lawn and i keep getting stuck on this hill. now this happens alot. and i get REALLY pissed. but i mean i hardly ever get mad if something dosent work so it must be because I'm hot right? i mean i get REALLY hot mowing my lawn and its pretty much the only time I'm angry. so why is that? does anyone have a smart long thought out answer for me?