When I was in junior school, many years ago, we had a head teacher that none of us liked called Mrs Wildee (not sure if that was the correct spelling). We called her "the Wildebeast", but we were prudent enough not to call her that to her face :-)
That's a very rude thing to say. What did she do to deserve that?
Was that a pun based upon her name? We'd do the same but just without the courage to say it before any teacher's face.
I'd call that prudence rather than lack of courage lol