Things that make me grind my gears in Pokemon:
Opponents who abuse status moves a lot, it gets annoying really fast.
Getting affected by status conditions like burn, paralysis, poison and sleep. Ugh...
People always requesting Level 9 and under Legendaries on the GTS.
Being forced to use a useless HM on a good Pokemon or swap something for an HM Slave.
Opponents using berries that weaken a super-effective move, I see them used way too often in the PWT.
Berries that trigger in a pinch, they can catch you off-guard if you're not expecting it.
Battling a strong Trainer and you can't seem to land a critical hit on them.
Fishermen with 6 Magikarps, they make me rage just as much as Marriland does.