Oh yeah, I can often be doing just about anything not thinking about sex, then out of nowhere my balls throb and I just gotta empty them.
Years ago when I worked in bars I went to the staff toilet to wank. A girl I worked with who I was flirting with had her bag in there while she was working the bar. I looked in and she had stuff packed to go to her boyfriends after work and there was a gorgeous sexy black satin nightie in it. I pulled it out and used it to wank off with til I ejaculated my heavy load all over it. Then put it back and went back out to flirt with her some more.