Sports, specifically watching them: I just don't understand the appeal. Playing them... I get. Watching them if someone you know is playing... I get. Outside of that, though, I just don't get it. They've always been extremely boring to me to watch, and to the best of my ability I still don't get not only how people pick favorite teams/players... but get SO passionate about them. Originally I thought "Oh, they favor the team for their state"... but that just seems silly, and it doesn't explain why people like my dad (who's OBSESSED with football and the Cleveland Browns) chose that he likes the Browns and hates the Bangles... when he doesn't live in Cleveland or Cincinnati. I dunno, sports in general just completely escape me.
Chocolate: This isn't even something I don't understand, I just don't like chocolate. There are SOME chocolates I think are really good, but even then I have to be in a very specific mood, usually don't eat much of it, and most of the chocolate I like... is apparently considered bad, while more popular brands... I find disgusting. Go figure.
Lord of the Rings 2 & 3: In all fairness... I really liked Fellowship of the Ring, and I am a HUGE fan of the Hobbit. I love fantasy, especially medieval fantasy. Two Towers and Return of the King, though... I just do not even slightly get why people love them so much. Be they books or films, they're just... completely dull, overly padded, and completely devoid of most things that made the Hobbit and Fellowship so great and memorable. I guess it's because the Hobbit and Fellowship were actually about the Hobbits and adventuring, while Towers and Return push that out of the way as a side plot to focus on Aragorn and medieval politics. It's always just some army fighting another army, someone's king then someone else is king, etc. They both feel completely lacking in adventure and charm, and I honestly don't think I could stand sitting through either of them ever again.
Parties: I'm in agreement, but possibly for different reasonings. While I also don't mind social interaction, I just don't understand how typical parties (especially 'college' style parties) are meant to be fun. People stand around... trying to scream over bad music that's way too loud, which in turn makes everyone's talking louder... all to basically do the exact same thing you could do with just a small group of friends minus all the irritation the 'party' element provides. Maybe there's just a whole side of it I'm completely missing, but for the most part parties just baffle me.
Country & Rap/Hip-Hop: These are both genres that almost everyone I know loves, and I just... I don't get it. I find both genres to be absolutely terrible 90% of the time, and while I truly am for people liking what they like... I'm shocked more people don't dislike this kind of music. I don't expect everyone to hate it, but when almost everyone around me loves... it becomes confusing.
Twitter & Tumblr: This isn't so much of a 'dislike' thing as a... "I don't get the appeal" thing. I'm fine with them, they don't really put me off or anything... I just don't get anything out of it. I've been signed up for both in the past, and I never feel compelled to keep up with it or inspired to really do anything on them.
MMO's: This might sound hypocritical because I actually played RuneScape for years and still do occasionally, but I only play(ed) RS because it's a fun little passive hobby. I never got 'super' into it and played it hardcore. I never dungeon raided end game dungeons, power leveled to max out my character, etc... I just play(ed) it because it's something easy and casual to do while you're doing something else. Virtually any other MMO... I just don't get it. What's fun about them? They're constant management, constant grinding, and the actual gameplay has always seemed incredibly empty and lifeless to me. There's just nothing appealing to me about stacking numbers and grinding to higher and higher levels just to go on repetitive dungeon raids to get the best armor, only for an expansion to come out and require you to do more of exactly the same thing. Maybe if I found the actual core gameplay fun... but I don't. It feels like constant work and management to achieve... more work and management.