You know something's going on, but you don't know what it is
1) Pot. I just don't get it. Tried it a couple times in college, and it basically made me bouncy and hungry. I later realized that being 19 made me bouncy and hungry, and didn't involve a federally controlled substance. I switched to booze and never looked back. (Alcohol, of course, makes me erudite, insightful, witty, and sexy. At least until the next day, when someone tells me what actually happened.)
2) Cigarettes. Full disclosure: I used to love pipes and cigars. I liked how they tasted, I loved how they smelled, I liked how they felt in my hand and my mouth. Unfortunately, I can't hold my nicotine anymore; I seem to go straight from the third puff to "oh, Mister Toilet Bowl, you're my only friend." As a prop, I can understand cigs; they do have the whole Bogie/James Dean thing going. But I always thought they tasted and smelled gross.
3) All auto racing except Grand Prix. Horses and humans are beautiful when they move. Motorcycles are cool, since you can see the rider. But for a car race to look good, you just gotta turn both right and left, in quick succession. Straight lines and wide turns? Booooooo-riiiiiiiiing. Frank De Ford said on Morning Edition that NASCAR is basically just a movie car chase unencumbered by plot, but come on... imagine Bullitt or The Dead Zone or The Blues Brothers if they only turned left.
4) P*r*s H*lt*n and the rest of the Professionally Famous. What have you done for me lately? Hell, what have you done for me ever? Do something first, just once or twice, and you can be a celebrity forever. But these people who think they get the spotlight by mere birthright? Let's treat them like the five year olds (or overgrown mascots) they are... just don't look and they'll go away.
(OK... on further reflection, I might be actively opposed to the Professionally Famous.)
5)The Brady Bunch. I simply don't understand why this is such a touchstone for my generation. Sure, it was amusing, but no more so than any number of other sitcoms I watched as a kid. Although I will say that if anyone has a bootleg of Boomslang singing the words to The Brady Bunch theme to the music of Freebird, email me and name your price.