Flirt.

You smile back, and swipe the bottle of beer to take a sip of your own. "To be honest, it was the sight of your ass. You look hot in my shirt already, and watching you grind on Matt, well... I just couldn't help myself."
Miranda takes the bottle back and pulls another swig. "Really? That's sweet of you to say..."
You laugh. "I don't know if 'sweet' is the word I would use, but it's the truth. You're.... you're a beautiful girl. I...think you're pretty hot." You stammer over the line, terrified to actually be admitting your crush. Miranda seems to think your lack of composure is cute.
"Aww... really? I'll never be as hot as Sarah, though. She's like a sex goddess. It's honestly frustrating being her roommate sometimes."
"I can't speak for anyone else, but I'd take you over her any day." You decide to just swing for the fences. You lean close, putting a hand on either side of her on the counter. Miranda's smile hasn't wavered: she's not stopping you.
"You're just saying that, because you're a nice guy..." you feel her fingers grip the belt loops of your pants, pulling you closer. You push all your chips forward, leaning down to plant your lips on hers.
"Mmmmf...." Miranda's hands slide easily around your waist, pulling your bodies together. You make out for a bit, enjoying the unbelievable moment that you never expected would happen. It wasn't even a dare!