If you go to a school where all the good parties are at frat houses then you undoubtedly know how hard it is to get in if you aren't with a bunch of hot chicks. This sucks because going to these parties is how you plan on meeting said hot chicks. A vicious cycle to say the least. Here are a few ideas that might help:
Dress up as a girl: Sound crazy? It is. Just crazy enough to work. Okay, it won't work. But maybe one of those frat guys will see the determination behind your eye makeup. The unyielding desire, the desperation in your heart. And then, you're in. Or, worst case scenario, you get your ass kicked and are banned from attending any frat party again, ever.
Show up naked: This helps if you're also bleeding, or shivering, or something equally vulnerable. When a concerned fraternity member asks you what's wrong, exclaim, "I was kidnapped!" They have to let you in then. They'll even lend you some kakis and a pink polo. Later, after you've had a few beers, point across the room at one of the frat guys that beat you in beer pong. "That's him," you'll say, "that's the man who hurt me."
Bring a gun/knife: Pretty self explanatory here, just threaten your way past the door. Be sure to keep your weapon out all night, people are definitely going to be trying to throw you out, especially the police. Weapons are also good for: Getting laid.
If none of these work try calling in a bomb threat. If you can't get in, might as well get all of them out.