This episode has been included in numerous 'top South Park episodes lists" and has been rated at first or second best episode in many of them.
It starts out with Cartman stupidly boasting about getting pubic hair, after BUYING pubic hair from a 15 year old named Scott Tenorman and the boys telling him that you're supposed to grow the pubic hair. Cartman goes to Scott and demands his money back, but gets humiliated by Scott more and then he burns the money Cartman gave him.
Thus Cartman begins his evil plans.
Sinc the boys think Cartman is a total idiot (and that they hate Cartman), they go ahead and meddle and snitch to Scott, so Scott plans to make Cartman's plan backfire. Cartman's original plan was to invite Scott to a chili festival with many people attending, get a pony to bite his balls off, and have Radiohead, Scott's favorite band, laugh at him when he cries.
So Cartman does invite Scott, and seems to have everything according to plan, except Scott spies the chili dish he gives Cartman by putting hair in the chili.
Then the fun starts, and the double backfires and fun! Watch the rest to see why this is the best episode...or at least in the top 3!