Yeah I know what you mean I've tried to always not lock out as well, I've known that for years....but like I said before when I said I cant explain in words they proper bend their arms. I'd say the two main exercises where people usually make this mistake the most is legpress and dips.
Maybe if I was better at maths I could give an example with an angle or degrees but I cant. I just know they do it completely wrong.
Infact out of my years in the gym I'd say this is the number one exercise I've seen people do wrong. Maybe thats because for some reason whenever I'm in the gym I only see certain people doing certain exercises which is strange. Seems like I always see everyone training shoulders and back, and sometimes chest, I hardly ever see anyone doing legs or arms.
I'd say side raises is number 1 exercise I see people do wrong, then squats, deadlifts bench and dips, most people in my gym do all these exercises with bad form.
I think it's because people go through stages, they start the gym and have bad form to begin with but then eventually those that choose to stick with it, and enjoy it, then begin to learn more and do more research and then realise form is more important then lifting as heavy as you can.
And yeah I've had those video's saved here for a while:
http://www.bodybuilding.com/fun/dorian-yates-blood-guts-6-week-trainer.htm
He's pretty much only bodybuilder I listen to now, I think he gives better advice then the rest, I'm currently doing that routine he has in those videos, well it's 99% the same.