Pretending To Laugh So You Dont Feel Stupid
--used as an alternate to "lol" when something isnt actually funny
ptlsydfs is commonly used in instant messaging :
abcXdef: funny story!
abcXdef: so at lunch, jane found a quarter, and i made her give it to me! lol!
cbaXfed: : ptlsydfs
abcXdef: good times!