The flesh threshold is the point at which a friendship becomes a hazy, undefined awkward mess filled with hook-ups and unanswered texts. After one crosses the flesh threshold, it is difficult if not impossible to return to the previous state of friendship.
Note: Sex is not required to cross the flesh threshold.
We can't invite Ryan and Rebecca to the same party - they're so awkward since they crossed the flesh threshold.
The threshold of finally conversing about poop that occurs between two colleagues which, once surpassed, is the indication of true friendship.
"Hey Macie wanna come over?" -Steve
"Yeah Steve, hold on lemme just poop first." -Macie
"Ah shit alright come back soon!" -Steve
"I might be a while, that burrito is gonna give me some killer Montezuma's Revenge." -Macie
"I'm so glad we just surpassed the Poop Threshold. I love you" -Steve