Just little pimples in the crease where your *$$ meets your leg? They're just pimples - compression blocks the pores, and that area is exposed to a lot of bacteria. Plus, when you're not riding, that's generally where the elastic of your underwear falls, so the pores still can't breathe. They can develop into saddle sores if left untreated. Clean the area really well before and after every ride (wipe with alcohol swab if you can't get to a shower right away, which will help with drying also), and get some antibiotic ointment on any pimples that do develop. When you're not riding, try wearing thong underwear or men's boxer briefs if they fit you - something that doesn't have elastic right there.
Speed comes from what you put behind you. - Judi Ketteler