donnie considers you his rival. it's the fact that you're intelligent like him and you're especially close to april. you're even better in combat than he is! he hates it.

even now, he watches from the porch in jealousy as you're able to spar with april to help her skills in ninjutsu grow. he could do better, right? he's been practicing ninjutsu for years with his sensei; master splinter.