The key to this achv is to hit each enemy type with the hair pick. Hair picks are those pink comb things that sometimes turn up in the Williams character that has the afro hairdo.
Throw them with X or B. It just has to hit the enemy, it doesn't have to kill them. Variations on enemies don't matter. For example any Abodo (white, black, Bimmy, Jimmy, the blue one) will count. Like wise white Williams, black Williams or the sort of Elvis-looking ones will count. Just get any one of them and you'll be fine.
The enemies (stole this bit from PS3trophies btw);
Skullmagaddon (this will get you an achv. Also you only need to do this one Stage 2, not the Stage 10 variant)
Hoverbizzle (regular or red TNT version will do)
Mecha Biker (Stage 4 boss. You'll have to carry a pick through the final airlock so use your heavy attack - Y - or specials - RB- in there. Get him after bike is destroyed, when he is on his feet)
Boa Boshi (easy to do on Stage 10 as there is a pick in the first smashable object just before he is introduced)
Plant boss/helicopter/giant tank boss are not required.
The bitch of the bunch is that flying girl (Roxy?). The easiest way to get a chance at hair picking her is to fire up Stage 7 (Some Kind of Lab). You can pick up a hair pick from one of the smashable barrels and she turns up pretty early. She was my last enemy to get so I can definitely confirm she counts for this achv. Nailing her is tricky though.
* "Here's a tip for Roxy - use jump kicks (Jump + X) to bring her down or stop her when she tries her charging attack. that should stop her long enough to make a better attempt with the hair pick." - Robster80 (from comments)