I would probably call this aggressive rather than desperate.
I was at a wedding reception that was held at a converted barn. I stepped behind one of the out buildings to take a piss. As I was walking back around the building, a friend of mine, Diane, pushed me backwards and then against the wall. She was a bigger girl and was able to move me, especially since I was confused at first. She leaned me up against the wall and went down on me for pretty decent blow job. She then put her finger up to her lips like she wanted me to keep a secret.
Shortly thereafter my ex, Beth, sat down. She is how I initially met Diane. When she asked how I was doing, I told her, "Well, you are not going to believe this, but Diane just pushed me up against the wall behind that shed and gave me a blow job."
She told me, "Oh, yeah, she does that. She is really self conscious about her weight, so what she ends up doing is blowing a guy and then she will masturbate thinking about it later."
It never happened again and the topic has never come up between her and I since. I do wonder who many times she pleased herself thinking about mine, though.