Turns out "mental orgasms" do exist, just ask Lady Gaga who says that her imagination is so vivid, she can have an orgasm just by thinking about sex. She tells New York magazine:

"I remember the first time that I drank out of an imaginary coffee cup. That's the very first thing they teach you (in acting class). I can feel the rain, too, when it's not raining."
"I don't know if this is too much for your magazine, but I can actually mentally give myself an orgasm. You know, sense memory is quite powerful."

Talk about titillating; no wonder she always has this 'O' look on her face whenever she's performing. Either that or she's faking it.

Mental orgasms may be scoffed at by some, and made fun of by others, but mental orgasms are pleasurable climaxes experienced by many. So, if you're a person who's lost hope of ever being able to orgasm due to some sort of disability, think again. With enough determination, the mind can do amazing things.

[NY Mag]