Comma or not

Esther Blodgett, a young Hollywood starlet married to an aging faded alcoholic matinee idol, writes:

Dear Grammer Genious,

Does the sentence “Next time you pour my gin down the drain[,] I’ll break your little goddamn neck” require a comma between the main clause and the dependent adverbial complement?

Signed, Esther Blodgett

Dear Miss Blodgett,

Nah.

The Grammer Genious

P.S. I'm selling your autograph on eBay, if that's ok with you.