Squeaky Clean refers to the fact that I'm apparently so much of a nerd / loser that not only have I never done drugs in my life, I've never even been offered drugs (either by friends or some guy at a party or some random seller on the street).
With that said, the rivals forum is the only one I use Squeak for. I usually go by Grillrat which has a better story.
Back in the early '90s, a few of the residence halls had little sports grill areas in them. One of them was in the McCutcheon Hall basement. My group of 20 or so friends all lived scattered around campus, but two or three lived in McCutchen, so we would go hang out there every night. It was a nice little area where you could get food, play cards, joke around, or even study (you could go to the back corner and it was quiet enough). In particular, a lot of us were on the fencing team and we practiced at the Co-Rec every night from 7-9 and then would hang out in the McCutchen grill till midnight or beyond.
There was some kind of fundraising drive in the McCutchen main office and they put out jars for each floor to donate to. The winning floor would get a pizza party. Most of us didn't belong to the dorm, but we still felt like being charitable (and wanted a chance to win pizza) so we asked for an additional jar to be put out for the basement floor. The secretaries were OK with it (after all, it was a charity drive). It was a "Penny Drive" where you could donate pennies to your floor for positive points or larger denomination coins to other floors for negative points. The collection went on for a few days, and on the last day, a bunch of us went over to Telhio and got about $100 worth in pennies. We thought we had it in the bag, but the secretaries, originally not thinking that we had any shot at winning, decided to intervene and started dumping any spare change they could find into our jar to send us below the 6th floor. We specifically overheard them talking about how "We can't let those rats down in the McCutchen grill win."
The name stuck, and from that day forward, we were known as the Grillrats. Sadly, we didn't win, but it was all for a good cause.
Unfortunately, they renovated that area back in the early 2000's and the grill went away (they turned it into a pure study area, I think). It was kinda sad that they killed it. Lotta good memories in there.