King of the Hill is mainly shown on Adult Swim, just that fact alone may scare parents away, although compared to, say, Family Guy, it's not bad at all.
It has the occasional innuendo, and of course the bursting with hormones teenager who is pretty much the source of some of it although some episodes are much worse. Some involve the main character being accused of renting dirty videos, and he must watch them to prove that he did not rent them. Occasional episodes show a naked person, either covered up for a split second.
Some episodes involve a murder of someone, with the crime being pointed on Hank. I believe there was a frame of a person in a dumpster, shotgun laying next to her.
In terms of drugs, there have been some highly suggestive episodes where the main character, Hank Hill, accidentally buys narcotics and is put on trial for them. Drug slangs are occasionally applied as well, things like being offered herb tea and responding that he didn't want to get hopped up on
"dope". Hank and his friends frequently drink beer, one of his friends a smoking addict who constantly smokes. There is also an episode where the entire family gets addicted to cigarettes. Hank once smoked marijuana on accident, thinking it was an average cigarette.
Language is probably the worst part of this show. Hank frequently tells his friends that he will "kick their ***", although aside from that, it's rarely used, aside from the occasional "B****" that showed up probably once. Other then that, language isn't used TOO much.
Good role models? Hank is an intelligent man with a nice family and house, but he has an anger problem. Bobby is a nice, funny kid, possibly okay to imitate, Peggy is occasionally up-tight and arrogant, although smart and friendly. His friends are smokers and clinically depressed people, one being just a mumbler which is fine although he gets into lots of relationship for just the, you know and then runs off. The chain smoker's wife always cheats on him, so not the best role models.
This show is great, although your kid may not enjoy it as much because it's not chock full of jokes and deals more with adult problems. It's okay for mature kids (probably around 13? If a bit more mature, that's for you to decide - I don't know, personally.)