Show me the funny money

Yesterday I went to the student cafe in MGU for a late dinner. Usually the place is open until 11pm, but a guy came out from behind the counter and explained to me that the kitchen was closed early on Sunday night, and that the restaurant would soon be shutting down. I had a bit of a sore stomach and all I wanted was a Coke, so I asked the young man if I could just have a soda. He nodded and told me to take a seat.

A few minutes later he came by my table with a Coke and I handed him a hundred ruble note -- which, thanks to the dollar's decline, is worth about $4 USD. He takes the bill and walks away, and I flip open my laptop to check on rumors that the cafe has a free wireless internet connection. Two minutes later the guy appears at my table, holding a bill with a missing corner. He says, "Sorry, but this bill is no good. The bank won't take it. Do you have another?"

Immediately I recognize that I'm being played. I didn't get a good look at the bill I gave him, but I'm pretty sure it wasn't missing any pieces. Even if it was, he's heard me speak with a limited vocabulary and knows that I don't have the linguistic capital to spend on an argument about this. And any lingering doubts I have about whether or not this is a scam are erased when the young man's face contorts into a wide, mischievous grin. Now I know that instead of getting change for me, he's spent the last minute swapping my 100 ruble note for this invalid bill. As best as I can reason, somebody must have pawned this bill off on the student cafe earlier in the day, and ever since the wait staff has been looking for an easy mark who won't protest when the exchange is made. I look him in the face, promise myself that I'm going to find a way to make him pay sometime in the next two months, and hand him another hundred.

I'm left with one question about this little scam, though. Maybe one of my dear readers, experienced travelers that they are, can explain to me why somebody tore off the corner of this bill to begin with. The bill is older than most now in circulation, but it doesn't look like a fake: it's got all the watermarks and microprinting that appear on authentic currency. What I don't understand is how someone would profit by ripping the corner off of this thing, whether it's the real deal or not. Any ideas?