Well, I finally got a chance to go back to Blimpie and talk to someone. I went at a later time when I knew those girls wouldn't be working, and asked for a manager. And apparently, from what the guy working there told me, they don't actually have a manager, which might be part of the problem. The "guy in charge", so to speak, is just the head of Dining Services on campus.
But I got his number and gave him a call. I mentioned the drink thing, and that they're pretty rude in general, though I accidentally left out the staring-and-no-greeting thing... but from the sounds of it, hopefully that won't matter, as he's going to "have a talk" with them about it. Thanks for the suggestions. :D