Abbreviation of I Swear To Mother Fucking God. Similar to “I Swear To Fucking God” istfg, in that it is an escalation of the original term “I Swear To God” istg. A very dramatic phrase to be used only in exceptional circumstances.
John: I wrecked my car Dave: ISTG John, again?
John: I hit yours.
Dave: ISTMFG
Either liquid niquil or any liquid drink with melatonin, Ashwaganda or other sleeping aids in a liquid form. If warm tea helps you get to sleep that could be sleepy juice too.
I could not sleep so I chugged some sleepy juice and now I'm so tired and sleepy.