The undecorable walls of the old house were covered in peeling paint.

The room was undecorated, with plain white walls and no furniture.

The undecorative walls of the room made it feel cold and unwelcoming.

She is undecorating the Christmas tree.

She undecorates her house every year.

She decided to undecorate the Christmas tree and go for a minimalist look.

He behaved undecorously at the formal dinner.

His undecorous behavior at the party shocked everyone.

Her undecorousness at the formal dinner shocked everyone.