I think my girl's sluttiest activity is going to a bar or club and fucking or sucking a random stranger she just met that night right there, usually in the bathroom, car, etc. Seeing her flirt with them and then coming back to the bar or table when she is done is sooo hot to me. A while back she was wearing a nice sexy dress and flirting with a guy. When she came out of the bathroom with him she looked like a hot mess - mascara running, hair messy, and she was holding her dress together to keep herself covered up because it broke at the top. Everybody in the place could tell what she was just up to. When she came back to the bar I thought she was going to say something about how hot or amazing it was or crack some joke like "how do I look?" but instead, the first thing she said was "I have to buy cheaper shit." I laughed. Ever since then she bought a lot of stuff from Yandy because it's cheaper, And we try to remember to keep spare clothes in the car in case her outfit gets destroyed again, which it has.
But that's what I consider to be her "slutwear." Although lingerie makes sense too.