Post the mods that you like and the ones that you dislike.
I'll start...
Worst Mods
1. Fender Trimming. 
It looks like crap and your better off to just get a lift. (not a body lift!!!)
2. Window Stickers/Bumper Stickers. 
Especially the zombie ones and those dumb stick figure family ones. Most of them look nerdy or high schooler-ish or just lame.
3. Euro Tail lights. 
well, they're pretty ugly
4. Engine Swaps. 
Wouldn't it be easier to just get a truck that came with a v8 from the factory? I guess if your doing a totally custom build it's cool but if I was going to do that I’d start from scratch and make a tube buggy lol
5. Rust.
lol not really a mod but happens from lack of body care.
Best Mods.
1. New Parts.
Especially parts that are better than stock factory. For example, swapping auto hubs for manual.
2. Exhaust.
Only if it doesn’t sound like a ricer.
3. New Paint Jobs. 
(professionally done, no spray paint unless its camo lol)
4. Bumpers.
Nicely made ones that don’t look like they came out of a junkyard lol unless that’s the look your going for.
5. New Headlights.(and headlight protection film)
I just got some and they are much better!!!! no more yellow lol
6. New Tires.