How should I ask my boyfriend to formal?

i was considering having a group of friends wait somewhere like at a train station, each of them with a letter written on their stomachs that spells out FORMAL? and have them flash their stomachs when we walk up to them as a way of asking him to formal...
is this lame or embarrassing... I was also considering maybe doing it at my house or something so its less public....
hes a funny guy so he will probably appreciate its meant sort of jokingly..
thoughts? any other suggestions...

Gather a bunch of your friend's have him gather him somewhere spicific, hide behind your friends and have them hold up signs that say Will you go to formal with me. or something funn wahtever im sure he'll be like hell yeah! haha. try hit you never live until you try.