Akuma no Riddle was the anime I dropped after watching the 1st episode. After the episode ended I knew I had enough.
Another anime I dropped in the first few seconds was Ladies versus Butlers! The reason I dropped it so fast was a shower scene of a nude purple-haired female in the beginning of the show. I knew I did not want to get invested in this show after viewing it.
For me it has to be Macross Delta. Maybe I'll revisit it one day, but the first episode left a really bad taste in my mouth. I've watched a few Macross series before, and the power of song has never bothered me too much. But when the singers are flying and dancing in formation as a magical girl idol group in robosuits in the middle of an otherwise serious battlefield? This is next level cringe.
EDIT: Note that I watched the episode pre-release, so there was at the time no further episodes to watch. I didn't drop it so much as never picked it back up upon TV release.
-Minami-ke, is supposed to be comedy, but I really didn't find anything funny about it.
-Girls und Panzer, not really appealing in any way. Might have liked it more if it had a mecha theme instead of tanks.
-Sakurako-san no Ashimoto ni wa Shitai ga Umatteiru, utterly boring. Found nothing to like about it, other than the pretty background art.