For me it's 0% because there's no such thing as a dumb question!
Now that I think about it it's really weird people who block me post in my threads because I can't upvote them therefore it's obvious they blocked me. That's really strange. I can't even endorse them. Wow. That's hardcore.
A lot. I can't really put a percentage on it, but I'll list some:
1. Thinly disguised rants. These aren't really questions----someone just wants to bitch about something and have people agree with them. Most often they come in the form of hating women.
2. Graceless generalizations. Obviously not all people are the same, so when someone asks, "Why do guys/girls do x?" Well, not all guys/girls do that thing.
3. Repeat questions. Questions that get asked over and over again, sometimes multiple times a day. Penis size questions are a good example of this.
4. Why-don't-you-google-it-yourself questions. Sometimes people ask questions that they could have googled the answers to faster than posting it/waiting for a response here.
5. Vague questions. People sometimes give a tiny bit of information and then ask, "What does this mean?" or "Does he/she like me?" There is absolutely no way we could know, and especially not with that small amount of information. This also includes any questions where the answer is: "Ask him/her" or "Talk to him/her about it". We cannot read your SO's mind, you need to learn how to communicate with them.