I know there's probably quite a few of these, but the one I've encountered is just begging to be mentioned. It is such a pain in the ass that I cannot beat it, I believe that if I rant about it I may get it out of my system. Here we go.
So which boss battles piss you off the most, due to the boss using cheap/dirty tricks and tatics?
In Mafia 2 you have to fight Derick near the end, he closes the warehouse on you and has 6 guys with tommy guns attack you while he throws an unlimited supply of molotov cocktails. This wouldn't be so bad if the game didn't blatently cheat all the time. Derick hides behind cover that actually manages to cover his fat ass and throws cocktails, up to three at a time. It doesn't matter if it hit you or not, it will do damage, there's no shockwave assosiated with a molotov so that's ruled out, the fire could be at the other end of cover and still hurt you. The fat cocksucker cheats, it's bullshit and as George Carlin said, "it's bad for ya".
So which boss battles piss you off the most, due to the boss using cheap/dirty tricks and tatics?