Unless you're an Britney is deceptively difficult.
2. Mariah is near impossible.
3. If you're even considering Whitney you've had far too much to drink and ask get a friend to help you into a taxi.
4. If you can dance, distract from your voice with your stunning moves.
5. Avoid Guns N' Roses unless you are prepared to do extensive air guitar performances.
6. If you know you genuinely can't sing, pick something that no-one alive can resist singing along to. Sweet Caroline or Don't Stop Believing (if you can still stand it) are your best bets. That way everyone else's voices will drown yours out. Hopefully.
Personal tale ahoy:
I cannot sing, but I did learn all the words to Wild Wild West by Will Smith while at university meaning I can get by in karaoke emergencies without having to sing a single note in tune. I can also deliver the song as a monologue - something which once impressed my sister on a long car journey and then upset her as she realised exactly how long the journey was and exactly how long I was prepared to recite for.
I am dealing with this issue by learning all the words the The Bad Touch by The Bloodhound Gang but you can either exit quietly/triumphantly after your first song or be prepared to join everyone else in a rousing rendition of Barbie Girl.