My girlfriends bought an extra pack of diapers for me and we spent 45 minutes or so writing goofy things on the diaper. They were meant to make my husband and me laugh when we had to get up for that 3AM change.
Some of my favorites were "Get it while it's hot!", one with a poo and flies drawn on the back, "Danger!", a skull and crossbones, etc.
The diapers don't last as long as onesies, but they were one of the best presents.