I'd say worms because they are associated with poo and bums. We've had TWO doses of the little fuckers so far...obviously reinfection despite my OCD at home.
We haven't had nits yet though so perhaps it's unfair of me to judge like this.
All I know is I DETEST parasites of any sort. Apparantly over 70% of living things on the earth is actually a parasite. Nice huh? Glad we're in the 30%.