A Czech art group has replaced the flag flying above the presidential palace with a huge pair of underpants in protest against President Milos Zeman.
Three men clambered onto the roof of the the official building dressed as chimney sweeps on Saturday. They have since been arrested.
The Ztohoven group said the new flag was for "a man who is not ashamed of anything".
But a presidential spokesman attacked the "desecration of state symbols".
A posting on Ztohoven's Facebook page listed a number of reasons for the protest, citing what they called Mr Zeman's support for "dubious dictators" and remarks he made suggesting he opposed disabled children being taught with non-disabled ones.
The red colour of the underpants is an apparent criticism of Mr Zeman's closeness to China.
Mr Zeman has previously been pelted by eggs amid anger over his support for Russia during the Ukraine conflict.