what does red tide mean in slang ?

Answer 1

A menstrual period.

The Crimson Tide is a football team (in Alabama? I think it's in Alabama.)

A literal red tide is an algal bloom caused by fertilizer or waste runoff that makes seafood unsafe to eat.

I don't often advocate changing nicknames, but yours is rather unfortunate. You might pick another.

Answer 2

The slang "red tide" is the encroachment of communism (the "reds").