What I Loved
I think the very basic, yet believable premise and attempts at misdirects make this a potentially great exercise in a sort of minimalist style of storytelling. It reminds me of sketch comedy - which I suppose it is - but, as I said in the summary, something I can't quite pin down makes me think of Vaudeville or the kind of sketch comedy people saw on variety shows in the fifties and sixties, in particular. The ending may be a little easy to predict, but it's still very satisfying as written.
What I'd Love To See
I don't really see anything written in the wrong way, necessarily, so these are just suggestions from having done and possibly still doing some of the same thing(s), which are always easier to spot in other people's work than our own. Thus, you could easily disregard all of this and still be just fine. :) Otherwise, this IS a short script, so I've found that stage direction and dialogue that is as minimal and efficient as possible leaves room for more to be done in the script within the same number of or even fewer pages. For example...
1. The stage direction might be a little tedious in places. All three of the "young" men are basically the same types, and since it doesn't require us to know a whole lot about the characters to be entertained, you might not even need to name them all in the instruction. Though they don't all come in at once, you could probably get away with just briefly describing Michael in a one or two line piece of instruction that could include something like, "The first of three young men having arrived, MICHAEL nervously flips through a magazine in the waiting room when...," "ENTER..." so-and-so by name should suffice for the rest because we already know there will be three and lines using their names and, particularly, the line, "Did Denise sleep with the entire fraternity?" tell us and the director what we need to and kind of already know by then.
2. Some of the dialogue, particularly in the first two pages, may be a bit on-the-nose. "Hey, Anthony," could probably be lost. We already know who Michael is, where he is, and that Anthony is a peer because of age, body type, and the line that identifies both as fraternity brothers or, at least, college kids. Making the first line the one about Denise getting to all of them might be funnier as well as quicker and would set a good pace and tone for the rest. Also, while it's probably more realistic as written, we also don't necessarily need to hear the Nurse tick off which room each enters. Since her function already seems to be that of a potentially or semi-imposing authority figure, the part may fill that function better if she speaks LESS, simply pointing each one to their rooms like some prison guard that doesn't think the prisoners deserve to be spoken to by name or something.
3. Based on the kind of feedback that I usually get, I would nix what amounts to camera direction when it comes to Denise's entry. I understand why it's there, but this isn't a production draft and, because such comedy is usually better when paced as fast and deliberately as possible, being direct and efficient with the stage direction, in particular, could allow you to maybe do and/or add more flavor without necessarily adding length/pages. As I learned it, I try to remember that, except for basic things like one or two-word transitions, camera direction be left out or, at least, be more suggestive. Here, you could write something like, "Suddenly, time stops for the three young men as the young, bottle-blonde bombshell DENISE makes her entrance in spectacular fashion - her waxed and polished beauty a remind of how and why they're here!" You could easily do without the stuff about her being "waxed and polished," but that's just my suggestion given her specific appearance is directly relevant to why this is all happening. ;)
Again, this is all based on feedback I've been given over what has to be the last 20 years of writing scripts. Odds are you could be or are just fine leaving the script as-is, which is still good and entertaining.