nejsem z cukru

on(a) tě neukousne

You should tell your teacher that you don't understand--she won't bite you. (Oxford Idioms)

třešnička na dortu

The meal was perfect, the wonderful view from the restaurant the icing on the cake. (Oxford Idioms)

nemá smysl plakat nad rozlitým mlékem

His decision to resign was disappointing, but it's no use crying over spilt milk. We need to concentrate on finding someone to replace him. (Oxford Idioms)