Can sex diseases be transmitted, lets say, masturbating using a piece of clothing (any clothing) wore by a person with sex diseases?
Yes, unlikely but yes you can get something that way. I do not recommend it. I asked a doctor this question once and I'm just passing along his response.
It depends. Is the clothing clean, or does it have the other person's bodily secretions and such on it? If it's not clean, there would be a potential chance of catching an infection depending on exactly what you're doing with it.
The flat out simple answer is yes. You can slap qualifiers on it if you want, but the answer is yes so now you know what you need to do if you want to be as safe as possible.