Here are some sprites I could say that about:
Sprite: Boss Bass
Offending hacks: Any that contain it
I hated Boss Bass in the original game (SMB3), and I don't like him any better in SMW hacks. In fact, he's even worse in hacks, since you can't kill the custom sprite version with fireballs, shells, etc. like you can in SMB3. Then there was that horrible stage in ASMT with a super-fast Boss Bass that was apparently based off something in one of the VIPs...I never played the original VIP level, thank goodness, but I definitely didn't feel like trying to beat the ASMT version. (Boss Bass was bad enough at normal speed...WHYYYYY?!!)
Sprite: Fishin' Boo (boss version or not)
Offending hacks: Any that contain it
He was only in one level in the original SMW, and he didn't seem all that bad there. However, in hacks, he always seems to be placed in the most awkward and annoying locations, making it nigh impossible to get past him without a dozen or more savestates.
Sprite: Deadweight Bro
Offending hacks: Bowser's Valley
World 7 in Bowser's Valley was evil. EVIL, I tell you!! The Deadweight Bro and his kin, especially when more than one of them is on the screen at once or when one is placed in an awkward location, are very difficult to avoid.
Sprite: Cave-In Generator
Offending hacks: Super Mario World: Legend of the 7 Golden Statues
It was only used in one level (well, I haven't beaten the hack yet, but only one so far), but once was enough. The level wasn't *too* difficult before (not easy either), but having to dodge falling rocks that come down randomly made it MUCH harder. In some sections, if the rocks fell in the wrong place, it was literally impossible to avoid taking a hit. I really had to savestate-spam that section. It kind of reminds me of Blaze Heatnix's Nightmare effect in Mega Man X6...but Mega Man X can shoot and air-dash, and he has a health meter instead of having only 3 hits at maximum. It is just too dang hard to avoid the falling blocks when you already have a bunch of other stuff to worry about.
Sprite: Pitchin' Chuck
Offending hacks: Bowser's Valley, but probably others
I didn't have all that much trouble with Pitchin' Chuck in the original SMW except in two stages in the Special World. In hacks, though, I realized how easy it is to abuse this sprite...considering he throws a constant stream of projectiles that can't be spin-jumped or destroyed without a cape, there isn't enough space in between them to jump in between, and he only pauses his attack for a moment, he can easily be overwhelming.
Sprite: Venus Fire Trap
Offending hacks: SMW - 7 Golden Statues
I swear I didn't mind this sprite before playing this particular hack...this particular hack, however, really seemed to spam these things. Even SMB3 didn't have them in every level. He's kind of like a lesser version of Pitchin' Chuck, but his projectiles don't go straight horizontally, and he doesn't have to be standing on something. It's not hard to place one or two of these in a really nasty position.
Sprite: Thwomp Boss
Offending hacks: Almost all hacks that use it
I don't dislike the Thwomp Boss because it's overused...I dislike it because it is so flipping hard to hit! You have to be awfully precise with the Bob-ombs to avoid missing or getting damaged, and it only gets worse when the thing speeds up.
Offending hacks: A lot that use it, although I can't remember the specifics
See above. In SMB2, the bombs he threw didn't walk around, couldn't hurt you (except when they blew up), had longer fuses, and couldn't kill each other if they collided. He was also fairly easy to hit in the original game. In hacks...well, I think the Mouser boss I had the most trouble with was the one in The Tale of Elementia. It was positioned awkwardly way high up in the room, plus the thing took like 10 hits to kill.
I can't really think of any graphics or patches that I've grown to hate, although I can think of some music...I don't care much at all for most of the unsampled Yoshi's Island ports or any of the unsampled Super Mario Kart ports.
I'm working on a hack! Check it out here.