Ooh, let's see...
Extremely masculine 'lees. Like, I love /m tickling, but I'm still straight in all other respects (and yes, that's possible). I'm not saying I like only pretty boys and really effeminate guys being tickled, I just get a little turned off when the 'lee is really hairy, uber-buff and has an awesome lumberjack beard, y'know?
'Lees that are obviously faking. I remember one video in particular, an amateur one that looked like it was aspiring to be a professional, where the 'ler asked the woman he was tickling whether she was actually tickling or if she was just acting, and she actually admitted she was acting. That made it an awful lot harder to enjoy the video, knowing that she wasn't really being tickled at all.
Too much banter. I like a little bit of teasing, don't get me wrong, and I LOVE helpless begging from the 'lee, but when the two are having a full-blown conversation in the middle of the tickle session, it gets a little distracting.
Any tickling that doesn't involve either the feet or the genitals, aside from some very specific exceptions. My fetish is a little pickier than others; unless the tickling is super light and erotic and involves long fingernails, feathers, or tongues, the only spots I like to see tickled are feet and naughty bits. Those vicious rib attacks and armpit prodding and tummy poking just don't do it for me.
'Lers and 'lees that look at the camera. Focus on the tickling, dammit! I don't need you glancing over here to confirm that yes, I'm still rubbing one out to you! XD
Gags, especially of the ball variety. I know a lot of people like them, but they're a turn-off for me. Same with extreme bondage; stocks and hogties and spread-eagles are nice, but not all of that kinky black-leather hyper restrictive stuff...
Sudden switches to foot worship. If there are to be tongues involved--and I do hope there are--I'd much prefer it if they tickled, rather than eliciting those orgasmic moans. Foot worship can be hot as hell in its own fashion, don't get me wrong, but when I'm in the mood for some desperate laughter, I don't wanna hear erotic moaning.
And this isn't so much about the clips themselves, but if I'm watching a clip on a porn site, it's kind of ruined a little bit by all the gifs of anal and BJs on the sidelines. Probably not the point of this thread, but hey, it's a thing that ruins clips for me, so... nyeh. XD