I do not PUG ops often, but the biggest problems I've had with them are the extremely undergeared tanks who don't know how to tank. Second are subpar DPS'.
The worst DPS I ever came across in a PUG was a guardian. I inspected him and found out that he was wearing smuggler pants and boots, sage implants, shadow tank earpiece and so on. I think he just ran a bunch of FPs, needed on everything purple then put it on. lol I don't think it's possible to get any more noob than that.
Wow, that's incredible. I don't think I can top that one, lol.
@OP: I don't use GF for ops and rarely for FP's now. I don't need to suffer the stupidity for 5 BH comms. I've had a similar experience with a HM KP, though. I was trying to tell the tank how to tank Bonethrasher since he had no clue and then preceded to ignore me and wipe the group, repeatedly. I left, saying I was going to go do something else when he had the attitude to whisper me blaming me for being a "bad dps and wiping us then leaving". I guess it was my fault for joining their group, though. I soon learnt the whole server knew he was a noob.