masturbate about someone you're not that attracted to... at all? I'm incredibly sexually frustrated, I find so many people attractive. And sometimes it's friends that I have absolutely no attraction to but I think about one thing they do or say that fits into my "things that give me sexual arousal" realm and I have the urge to masturbate about them.
Myself had urges and dreams at times. Not sure your age but your feelings are perfectly normal. Don't worry so much
You are experimenting (mentally), it happens. Anyone with a libido, which is most people unless they have some physical or hormonal irregularity, masturbates. Your libido sends weird hormones around the body and messes with your bodily functions, it makes weird thoughts. It could be a response to something that you were taught to see as sexually arousing. Or it could just be the actions that you find attractive. I know that I don't find people sexually attractive, but I can find actions, fantasy, etcetera to be arousing.
