Shorthand for please, but nowadays since texting shorthand isn't really used, it has actually become something of a separate entity. It has made it into verbal speech, such as "lol", and is pronounced "plz" or "
pluz". In this context, in
in and of itself can be used to mean:
"oh please" used to call out one's bullshit.
or
"please no" a
subdued beg for mercy, usually from an online roasting.