This happens when you are speaking with someone that you really don't like and you somehow pay them a compliment which causes you to despise yourself for they now know that can recognize a positive quality in them. I have done this.
Emily: "Christine, I don't know how you made that situation work out for the best considering your lack of training. I guess you're just a natural."
Christine: "Thank you, Emily! I thought you didn't like me."
Emily: "Ummm. You are just fine. (in her mind - You dumb-ass doing the accidentally complimentary. Now she's your pal)
Basically if you say an idea, and a nearby parent/ teacher hears it.
Kade: Hell yeah, the teacher forgot about this homework!
Teacher: What a great idea Kade! Every one turn in your homework.
Kade: FML, accidental idea.
When two or more bros are in a testosterone-fueled activity, much like accidental anal, and unintentionally end up having an extremely satisfying and fulfilling workout.
Bro, you got some mad accidental gains from that dutch rudder you gave me yesterday.
When you try to say something to someone that sounded right in your head at first, and you end up burning them instead.
Just watch michael kelso accidental burn himself in that 70s show. He does it pretty often
when a woman doesn't know the pad/liner she is wearing has shifted & is now attached to her pubic hair, then pulls down her underwear too quickly, rendering a surprise bald patch.
I'm not sad, I just took an accidental trip to Rio & now my eyes won't stop watering!