Spoiler alert:  It is every night.  Never the less, this article does an excellent job breaking down the order of the which nights are better than others.

“It’s Friday. A glorious weekend of drinking awaits you. You can hardly wait. It’s not five yet, but you yearn to break free of work NOW and drench yourself head to toe in pure Thunderbird.

Yesterday, I noted that Halloween falls on a Saturday this year, and I recklessly declared Saturday the drunkenest day of the week. Ah, but is that always necessarily true? Let’s start this exercise by stating flatly that the best day of the week to get drunk is, of course, ALL OF THEM. There’s no wrong night to get drunk! That’s the beauty of alcoholism! But, for shits and giggles, let’s rank the nights of the week for drinking purposes anyway.”