The Bavarian State Opera is capitalising on the vociferous disapproval that greets every new production (and some old ones too).
Online, you can buy a T shirt to tell the world that your boos are the best (sadly, ladies sizes only).
The Munich shop carries a few more options, including a straightforward 'Buh' for those confident in their opinion, and more equivocal 'Buh oder Bravo?' for anyone less sure.
Negativity doesn't come cheap though; the well-made but plain shirts retail at a Man U-esque 29 euros (£25).