I got excited when I saw a picture of a boy sticking a pencil into his pee hole. Is that dangerous?

Yes it is, so I advise against it. It’s very easy to damage the urethra that way, especially if there is a stricture in your urethra or if there is scar tissue. When the object you insert is not free of germs you also run the risk of infections. Daily objects are not sterile, even if you clean them. It can cause a bladder infection or problems with your kidneys. It can also hurt afterwards and give a burning feeling. In short: don’t do it. You can fantasize about it if that is exciting, but do not put it into practice.