Little annoying 6 and 7 year olds putting my hardware through more beatings in a day than I gave it in a year because they just wanted a reason to fight with each other piss me off. But I love em, so I can't really be all that pissed at em.
If you mean stuff that pisses you off that you STAY pissed off about, though...
Cockfaced drunkard 40something year olds who like to manipulate and mentally abuse women and punch holes in houses, shed doors, and vehicle casing piss me off.