The Masturbational

I was in an art museum in the Netherlands with my family. It was in a big warehouse and my sister had on a really thin crop top so I could see her nipples through it which really turned me on. I had a hard on for most of the day until I could not wait any longer so I rushed to the toilets and pulled out my cock and started masturbating. It didn't take long until I cummed everywhere. When I was done the man in the next stall said " it sounds like your having a good time" and i replied "come and join me if you like" which he did and then we both masturbated together.