Anything that isn't a Yeti.
Any bike model named after a sex act or rude body part and has the name in massive letters somewhere on it. (That's basically all Coves then... Handjob, Stiffy. Very amusing if you're 13 years old)
Most Konas (because of the daft names)
Anything with less than 10 cogs on the back (unless it's an internal geared hub)
I tend to buy frames and build up with carefully chosen parts. I like Sram rear mech, cassettes and shifters, Shimano BB and Crank. Crank must have steel rings (2 x 10), Sram chain, Avid brakes. Shimano spd pedals (cheap, easy to use, solid, reliable, CHEAP). Split tube ghetto tubeless.