What is Thriggyback?
A three man piggyback.
A person on a person's back on a person's back.
Fiend1: let's do a thriggyback!!
Fiend2: a what?
Fiend1: a fuckin thriggyback! issa three man piggyback innit.
Fiend2: oh....
See thriggyback, piggyback, back, piggy