1. Do not actually try to sit on, or ride the cat. As funny as it is, they don't really like it and it's not technically what their owner meant whey they asked you to catsit.
2. Don't bother making friends with the cat. If the cat wants to hide under the sofa for 3 days straight, let him. It's better than contracting cat-scratch fever the old fashioned way....trust me.
3. If the cat insists on being served its wet food in your shoe, comply. There are grosser things the cat could be doing in your shoe. Again, trust me.
4. If the cat appears to dislike the movie you are watching, trust it's opinion and shut the damn thing off. The ensuing cat showdown just isn't worth another 20 minutes of Sandra Bullock. As cats are not allowed in Blockbuster, be prepared to leave the remote control wherever little paws can reach and watch cable at the cat's mercy - if the cat shows a preference for late night latino talk show hosts who appear to have traded sex for money or blow for the past 60 years or so, then so be it.
5. Do not do yoga in front of the cat. Don't even wear yoga pants in front of the cat.
6. Don't fall for the "but I'm still hungry" look - it's a dirty trick that all cats play. The cat is NOT still hungry. However, when you overfeed it, the cat will overeat, until it's little belly is extended in bloated, resulting in explosive cat diarrhea the next day. Not only will you spend the next 3 hours scrubbing your friend's carpet, couch, drapes, and improbably, the top shelf of a very large book case, but you'll also have to kiss goodbye your favourite pair of Chucks (but for hygienic reasons, don't actually kiss them goodbye, don a double pair of latex gloves before incinerating them at your nearest toxic waste dump).
7. When you give the cat its shot of insulin (yes, the cat is diabetic) and suddenly the cat goes all crazy-eyed and starts acting like a donkey who just finished drinking a bucket of beer, call the vet immediately. Don't stop to take hilarious-but-insensitive video of the cat with your cell phone, then post it to Youtube, then call 3 of your easiest-amused friends to come over to see "the diabetic cat who's shit-faced on insulin". And when you finally do get to calling the vet, who says to come immediately, do not stop of slurpees, or to buy a new pair of Chucks.
8. When you get to the vet's office and she asks what kind of cat this is, don't say "um, orange?" and don't guess that his name "might be Charles", because the cat will turn out to be a girl, and you'll look like a dumbass. Remember that little note on the fridge back at your friend's apartment? The one with all the cat's details, that says something about what to do when the diabetic cat reacts badly to its insulin? Turns out, you should have brought it with you, or at least read the damn thing instead of mocking it, and your anal friends who wrote it - both sides, front and back! - about an effing cat, christ it's just a cat, do they think I can't sit and watch their dumb cat?
9. Also, it turns out that vets politely require you to have cats in some sort of carrying case when you go to their office, and frown upon just throwing the cat in the trunk of your car, and then trying to coax it into the office via an intoxicating trail of fruit loops (as a matter of fact, fruit loops don't go over well with diabetics in general).
10. Never catsit for people you actually like and expect to remain friends with. When they get home, receive the vet bill (and the bill to replace your Chucks, naturally), see that their heirloom turkish carpet is harbouring telling stains, and that you went through a 25 bag of cat food in 36 hours, and that their beloved Mrs. Fudge (Mrs. Fudge? Seriously? You named your cat Mrs. Fudge?) is recovering from diabetic coma and deals with the emotional trauma of having the 2058th highest-rated cat-related Youtube video by shredding random pieces of furniture....well, let's just say that you probably won't be receiving a thank you card in the mail anytime soon. Cat people can be such snobs.