How the fuck do I get these things off? (without cutting them)
With great difficulty.
However, a few methods that might work:
- If you have an air-compressor, do what the bike shops do and blow inbetween the grip and the bar and shimmy it off (perhaps you have a friendly LBS that could help?);
- With much sweat and cursing, wriggle/stretch them off the bar as far as your frustration levels will allow, then roll them back over themselves until they finally come off;
- Don’t remove them, simply get new bars and stem.
OR you could spray some WD40 or similar product into the grips. Wiggle the grips to get the product to travel to the end and you should be able to pull it out of the bars no problem. Wash the grips and wide down your bars after. Works for me.
I’m all for #3.
If you’re at the stage where you don’t like your grips anymore then you’re definitely at the stage where you’re over your bars too.
Chuck em and get new ones. 
I use hair spary to get mine off (and on), and it’s easier to clean than WD40 or similar…
2nd vote for the hair spray option. Good for gluing them on too, as it dries out and sets if left overnight.
Just did mine yeaterday.
Stick something like a chopstick as far into the open end of the grip. Squirt lighter fluid or hairspray or whatever into the gap. Then wiggle grip and push stick further in and repeat. Not to much effort required.
1 - Struggle.
2 - Rip skin from your hands.
3 - Say, “Fuck it, I’ll just sell 'em like this”.
4 - Hand them to Nick and watch him pull that grip off like a used condom.
compressed air
EEEEIIIIIWWWWWWWW
Easy. Get small screwdriver in the end closest to the stem. Squirt water in there. Move the grips around. Squirt a bit more water in. Pull them off. Dry them off, put them on new bars.
No mess no fuss. It just works.