Left on Jack's desk [A small, ornate box containing a pair of instant underpants, which has a concealed false bottom concealing a gift card to a nice restaurant in town. There is a note beside it.]
Jack -
I'm guessing you opened the box before the card and are now confused. It's a trick. If you manage to figure it out before Valentine's day, I suggest you ask your lady friend to dine with you. The underpants are for in case you wet yourself in the process. Always prepare for emergencies. Happy early birthday.