Fred and George had been tasked to make a ridiculous-looking crown and they were delivering. Sure it was last minute (really last minute) but nothing a little magic, transfiguration, and blackmail couldn't solve.
The end result was (purposefully) badly crafted and (purposefully) smoked and (purposefully) stupid looking.
It was their best non-explosive creations to date. How best to declared yourself the Queen of something stupid than with a stupid-looking crown?
Gred and Forge were mighty proud to put the too big crown on Hermione's head while they each kissed a cheek.
There was mischief a-foot and they would use her as their in.