"It's Lacus!"

Shinn steals Lacus' dress so she can't go onstage, only to run into Kira and be forced to put the dress on and pretend to be Lacus. Somehow, despite how off Kira can tell things are, he doesn't realize "Lacus" has the wrong hair and eye colors or that "she" is really someone he's met before.

Example of:
Paper-Thin Disguise