Giri is short for 'giririsss', commonly known to many as someone who pikes from everything. A giri will agree to meet someone/somewhere, and not show up, thus piking.
you: Hey giri, wanna come over?
giri: sure, meet you at 2pm?
you: cool, cya then!
giri doesnt turn up at all.
you: oh well, i shouldnt of trusted giri showing up!