It means when a person thing another human has a big butt
"OHSHETHICC DAD"
"Ohshethicc" produced ooh-she-thicccc
It is used to define someone of glory or hotness. Also to define someone who is thiccer than a snicker.
Friend: ohshethicc!
Friend 2: ... what?
Friend: she is hella thicc.
Friend 2: 🙄