Set in the same universe as Zecora's Big Surprise, though you don't need to read that to enjoy this.

Spike's visiting Canterlot to assist Princess Celestia with some heavy-duty paperwork. It's about as he expected: mindnumbing boring. So when he gets some time to himself on his third day working, he takes the opportunity to relieve his growing, ahem, stress from having to sit around all day next to Princess Celestia's heavenly plot filing paperwork and sending letters. He thinks the place he's chosen to do his naughtiness is secluded.

It's not.