Basically something that disgusts you, find embarrassing or unappealing (mostly) about the opposite sex.
1. Lisa: "So, my boyfriend and I had sex for the first time last night."
Natalie: "Really!? Oh my god, how was it?"
Lisa: "It was okay... but when he started climaxing, he farted! It smelled so bad!"
Natalie: "Ew!! What a turn off!"
2. "There was this random girl who danced with me at the party last night. She was so hot. But when she grinned at me at me, I noticed she was missing two front teeth. Immediately turned me off, man."
Things that will make what seems like a really good time in bed, into something unpleasant and embarassing.
"My ex does a much better blowjob than you"
"Is your mother/daughter dating"
"How much do you weigh anyway?"
"Can we get this on"
when u r really horny and suddenly u see something that takes the feeling away.
like if u see a girl and she starts giveing u a bj and ur like fuk yea this is so hot and ur excited and "turned on" and then she takes off her pants and has a dick and then takes off her/his wig and is a man then ur like wtf, want to go puke, want to kill it, and are "turn off"
when your penis is not excited or aroused.
the opposite of turn on.
That pedestrian walking across the street was such a big turn off for me.