I can think of a couple.
One time I was staying with some relatives, my grandma, actually.
She sleeps downstairs instead of 'her' room upstairs, which said told me I could sleep in.
Well, I was laying in bed, incredibly horny, so I jacked off in my grandma's bed. It was strange to say the least.
Another time I was at the dentist, to get my wisdom teeth taken out, and I was really nervous about it, so I rubbed one out in the bathroom there, thinking about one of the Dental Technicians (aka nurses). I wonder if they thought it was weird when the dentist and the same nurse were taking out my wisdom teeth and I got another hard on. lol