A lot of people get hung up on the word "slut." And, in a large respect, people should. It's an insult of tremendous magnitude.
Multiple sex partners alone does not a slut make. Want to be one? Here's a few things to do:
1 - Use your sexuality as a commodity. Unlike a whore, don't accept money, but use it to obtain goodies, favorable treatment, and to get your way paid. In many cases, the vague promise of a possible future hook-up may be sufficient.
2 - Talk often and frequently about your sexual past. Provide lurid and explicit details. Compare and contrast performances of current and past lovers.
3 - Always make sure your current thing knows that the minute a better catch comes along he's yesterday's news.
4 - Frequently vocalize your desires to "fuck the legs off" of other guys you find attractive in the presence of your current thing.
5 - Depersonalize the man you are seeing - make sure he and everyone knows he's your "thing" or "boy-toy." Never man, boyfriend, et. al. If you start thinking of him as a person, you might (gasp!) treat him like one.
6 - Hand in hand with #1, use sex as a weapon. If you don't get your way, withhold it. For added impact, go have a one-nighter with someone else. To keep things really exciting, do this randomly, hoping he'll apologize for something you didn't catch him at, and that he'll buy you something to make up.
7 - Deride every gesture your partner makes. Insure that he thinks he's always falling short somehow.
8 - Hold a double standard, and make him abide by it, or see #6.
9 - Constantly demand attention, and time it so that he has to choose between you and final exams, missing a trip he's been looking forward to for months, going to work on an important day, and so on. Don't do this in time to change these plans, do it as he's getting ready to walk out the door on that day. Pout and have a snit for at least a week afterwards. Go have a grudge fuck.
10 - Be constantly late, or change plans at the last minute without informing him. Claim you told him.
11 - Don't let him have any time to himself. Demand accountability 24-7. See #8 above as well. Claim that for you to do it is stifling and oppressive.
12 - Rehash the past at any and all opportunities. Magnify every detail, and ignore all evidences to the contrary.
Do all or most of these things, and when he walks out, you can continue to feel justified in thinking that all men are scum, and immature commitmentphobes.