If he's paying you a decent price....sell it to him.
After the check clears, find out where he parks the bike at night.
Go to Walmart, and buy a set of pink and white handlebar streamers like you see on girls bicycles. If they have a wicker basket with flowers, that's cool too.
Place the above items on the 'girly bike' late at night so he'll find them in the morning.
Any 'Barbie' stickers you can find are cool, also.