It depends on the situation. It's only possibly slutty if it was the first time. If it was an inappropriate relationship but the person was hierarchically superior to you, it was slutty. Otherwise, rape is a possibility.
On another note - this has always puzzled me... I have heard of women who will play mind games with a guy by sleeping with him ONCE, and then ignoring him. Anybody ever hear of this (I actually heard it called the "Johnny One Time" method)? I can see where it can be used for control but am puzzled to how much control it might get. I mean, in the final analysis, the guy still got some and still has bragging rights. Was this just some aberrant piece of data I picked up?