When the word "nasty" is used it conjures up something "bad" or undesireable, I've heard mother's chastise their children by telling them "That's nasty!" when the little darling is doing something he'she shouldn't do. But in the context of sex it can have an entirely different meaning; namely things yet tried or desires not mentioned. So, in truth, nasty sex can often be something we want but are simply too timid to seek. True?
"Nasty" is when animal like noises are coming from the room....stuff is getting knocked around.....wet with sweat....breathing like you are running.....if you overheard it, you would not be sure if it was a struggle or a passionate encounter.
Neighbors might dial 911.
Not every time, but there's a lot to be said for grabbing a handful of ass and just start ramming. If she yells for more, even better. But then there's other times when a nice, slow, get deep into her soul-type of afternoon is called for. But, yeah, dirty is damned good!
First time I made the decision to push my thumb up my girlfriend's ass while fucking her doggy. She was already breathing in rhthym to the thrusts and when I pressed my finger on her hole she sort of made a deep groaning sound and seemed to have braced herself. Whe it penetrated her ass she gasped and said "Noooooooo" but was grindng her hole back towards my finger while I snaked it in. I came really hard and she played with herself until she blew too. It was "nasty" because it was the first time for me and her reaction to it made it even hotter!