I have 10 gripes.
1. Having no real profile to speak of, or one that indicates your only interest is watching TV
2. Having no photo, and refusing to send one on when asked nicely
3. Profiles that indicate a cultlike committment to the ghetto that is dyke culture - with only interests being the L Word and Lip Service, and only pubs visited gay bars
4. Text speak, bad spelling and misuse of punctuation, or worst of all, no punctuation at all so every single paragraph sounds like one long sentence which ultimate sounds like the rantings of a psychotic madwoman which is probably what you are anyway
5. Photographs of pets, nature, soft toys, cars, sunsets. Especially annoying is ones you didn't take yourself.
6. Very obvious pervs. There are other sites for you. Go find.
7. Chatting incessantly for months, even years without ever agreeing to meet. Thats just time wasting.
8. Sending on your google talk, windows live or email information because you are too stingy to par for the site you are on
9. No shows when meetings are arranged. Half arsed excuses afterwards that are clearly not the truth.
10. And last but not least, indicating that you are open to friendship as well as looking for a relationship, but then backing out of this because you've got your own life already and are really only interested in a relationship. If you don't want friendship, then don't indicate it on your profile!
There are others. Indicating that you are single when you are not. Factual inaccuracies - false names, different locations, different careers, or pretending you've got a job when you don't. (Ok, why not just leave the field blank?) Another no-no is using somebody elses account. Don't laugh: an ex did that one to me, twice, to organise affairs.
Cultural coverups. Indicating you are out when you are not, pretending to have no children or not be married. Misrepresentations in general.
And finally, the worst of all, messaging somebody you already know, but haven't recognised!