Here are a list of things I have seen people do that I think "Wow, why in god's green earth did they put THAT on the their profile."
Feel free to add anything else you have seen.
1) 1/4 of their profile is ALL CAPS SO THEY ARE YELLING AT ME. Often about (see #2). I know of almost no one that enjoys being yelled at. While I am sure they do exist, I think they are more likely to look on a kinky web site, rather than this one.
2) 1/4 (or even all) of their profile is about the kind of person they don't want to meet, rather than about the kind of person they do want to meet. All this does is attract those people, not repel them. (It makes you look like an easy mark)
3) The profile mentions things they don't like - even once. I am a bit of a nerd, and therefore am likely to search for things like "nerd", "geek", "Sci-Fi", etc. It is annoying to do the serach and find someone wrote about how they hate geeks and don't email her if you are a geek. ALL IN CAPS, just to drive the point in, of course.
4) To put in a picture that does not truly represent how you look, or lie about your height/weight/job/wealth. They will find out on the first date, and it does you no good. I am short, and I do dislike the fact that so many women reject me for my height, but I do know that lying about it won't help the situation. If you are older, fatter, shorter, poorer, than your profile, says you are you may get more interest, but they will drop you quicker than you can believe possible. Weight can be off a little bit, and height can be off by as much as an inch, but more than that and people know right away.
5) Empty Profiles. Your looks may be your best quality, but there are more than enough pretty people on this website that the shallowest of men/women want someone that at least know how to write a sentence or two. Even if your English is poor (and you are looking for an American), write something in your own language and add a bit at the end saying you are learning English.