Crossword puzzle clue "something you should never say"

Something you should never say?

Something you should never do: Hyph.

Never, never, never

"There are some things you should just never tell another person," briefly

Treat instrumentally, as you should never do to a significant other

"Say Yes to the ___" (show I just made up where you vote on which lock of a woman's hair you should wear)

What you say right after you say something at the same time as someone else

Street corner things that tell you you can't park here, if you should stop, where to go, etc.