My god where to begin.
Fallout 3: Deathclaws and Sentry Bots. Not separate though, I can deal with that. It was just that outside of the Regulator HQ, there would always, ALWAYS spawn a Sentry Bot and a Deathclaw, that way, while I'm running around being stabbed in the ass by the deathclaw, I'm also being shot repeatedly. Also, occasionally, a deathclaw would spawn INSIDE the Regulator HQ. So yeah. Fuck you Deathclaw. Fuck you Sentry Bot.
Mortal Kombat Trilogy: Motaro, Kentaro, Goro, Shao Kahn, and Chameleon. I can't even describe the hate I feel for these characters. So I'm not. If you've played against them, you know.
Final Fantasy 7: Emerald Weapon. I didn't have the Underwater Materia or the "Missing Score" for Barret, so I got raped. A LOT. A LOOOOOOOOOOOT. Then I got "Missing Score" and killed the bastard in one hit a couple of times.
Final Fantasy 13: All the goddamn Eidolons. I hated fighting every last one of those bastards with a passion. I barely used them too! They were just collecting dust for about 80% of the game.
Kingdom Hearts: Sephiroth. I could handle that long haired bastard in the Final Fantasy 7, but in Kingdom Hearts, no. The first time I played Kingdom Hearts, it was by recommendation by a friend I was like "Oh Disney this is gonna suck," so I sped through it and avoided as many enemies as I could. Eventually, I beat the game at minimum level basically required to kill Ansem(I hated him too) then I went to the Coliseum and fought the Ice Titan. It was hard, but nothing killer. Then I fought Sephiroth. I had to grind for HOURS to reach a high enough level to beat him, and even then he still sometimes won. I still play that game though. And every time I do, I level as much as I can, that way, Sephiroth dies. Quickly.