When a guy is plowing a girl from behind, busts on her back, and writes his initials in the cum with his finger. Once dried, his initials will be printed in the crusty jizz canvas.
Hey bro, when I was banging my girl this morning I went to give her the ol' New York Crust. But before I busted, I looked down and discovered someone with your initials had already done it...
Dried bits of poo left on and around the butthole, formed as a direct result of waiting to long to wipe. Aforementioned "crusties" generally begin to form 10 or more minutes after final defecation (a.k.a. grand finale) has occurred.
Note: Flatulence exacerbates said condition as it tends to promote drying. Drying time dependent on velocity of flatulence, body temperature, external humidity, and PSI.
"Kind sir, I seem to have run out of TP. Could you assist me before I develop poop crusties"
"The recent Polly Shore article in the Times caused me to loose track of time, the result was a great deal of uncomfortable poop crusties."
This florida humidity is awesome, 30 minutes and still no poop crusties.