i found out a great way to put on bmx style grips (no clamps) you dry your handlebar surface then put zip ties around the inside side of the grip, then you just twist it on. with the zip ties helping you it's really easy. then when it's on there good you just pull the zip ties out 1 by 1. i use it all the time and it works perfect. for taking off grips i just slide in a flathead screwdriver and spray in some fantastic, then i just slide it off
hairspray...easiesy way...spray inside of grip,slid on, let dry for 15 min....ride
the zip tie thing does the same, you just won't have to wait 15min
I know it's an old thread, but metholated spirits works great, put a dribble in your grip shake it all around slide on easy
I learned a really interesting method of sticking ones grips solidly to the bar. Someone showed this to me at the motocross track but theres no reason you couldnt do this on a mountain bike. Take electrical tape and put about three layers on the bar end, covering the same length as the grip. Fill grip with gasoline and slam it onto the bar, let the gas evaporate for a few minutes and you will literally need a knife to get those suckers off.
If you've got the right tools then nothing should be that hard.
Bits that are seize/stripped/rounded are another matter. I think the worst I've had was back in the day when I worked in a LBS where we had a seized seat post. can't remember if it was steel on steel or whether it was slightly too big but it was stuck fast, had the bike stripped down to bare frame and the thing in a vice nearly tipping the whole workshop over trying to twist it free with heat guns etc. Ended up cutting the post level with the frame and the running a hacksaw blade down the shaft to cut it in half. That deserved a beer afterwards..