an anus weed is a cluster of anal hairs that have grown long and knot all up inside your bung hole, and when you wipe after taking a massive dump, the anus weed gets ripped out by the toilet paper, thus causing extreme pain and sometimes anal bleeding.
Frent : "Hey Kent, what took you so long in the bathroom? Jesus."
Kent : "Look man, my anus weed was yanked by the toilet paper, so my bung hole started bleeding all down my leg, and I had to clean that poopy blood off before I could come out."