So this happens because the urethra loses moisture and welds shut, then pee chooses the least-resistance path. If you can't pee sitting ('cause it's easier), one trick is to clamp your dick and push to pee, then release. The pressure will open the urethra wide and a beautiful, directed stream of piss will come out. Also, pull your foreskin back when peeing and clean afterwards with a dab of toilet paper. Fellating persons will thank you!