Justin Bieber, if you're reading this (and I like to imagine that you are), may I suggest an amazing "couples" costume idea???? Selena can go as Videl, and you can go as either Son Goku or a pair of dragon balls!
It's really just simple math here, folks. Selena Gomez + Justin Bieber = This composite image of a creature called Selena Bieber. Selena Bieber + Taylor Lautner = A look-alike that will haunt your dreams for all of time. MATH!