A wet fart, a fart in which upon being expelled from the anus, carries with it ass juice. Leaving your undergarments caught in the crossfire. A schlem can be due to relaxed sphincter muscles, i.e. bum love. If you are unfortunate enough to suffer a schlem, do not try and salvage your underwear, make sure you dispose of it!
"Aw man i've got 'schlem' juice running down my leg!"
"I hear Ian 'schlems' so bad, he has to wear a sanitary towel!"