Theo

A thong. A skimpy undergarment. First known to be used in Glasgow. A slang term deriving from shortening Theodore Long's name to Th-ong. Private code used by boys in classrooms.

Other known variations;
Paphitis
Rosevelt
Teddy

Marv: Did you spot the Theo on Tiffany in Biology.
Keith: PHWOAR. it was a frilly bad boy.

Tiffany: Does this Theo make my bum look big?