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1.
First time.

Originally used for referring to skateboarding, as in landing tricks first t.

Something to be called out before you do an act in which you believe you can land/do first t.

Also can be referred to sex, partying, fighting or can be used in a sentence just to boost up an event, or to show that you are a pro at whatever you are talking about. (Because you know that you will land it/do it first t)

If someone fails to do such an act where they had called it before hand to be a first t, then everyone around must stop and stare very seriously and say that it was not first t. The failure must also accept and admit that it was not first t.

Most people add on "all day" after saying first t, as this will boost the first t statement meaning that they will not only land/do said action first t, but they will land it/do it first t all day, if one were to do said action all day.
Sabz: Bro you skating after school?
Glover: Downskis bro rockin fakie heels son first t all day!
Sabz: lmao yes glover first t all day you knowwwwwwwww!

Sabz: How pumped are you for Guv tonight man?
Glover: You do not understand how excited I am right now, it's guna be such a good night man first t all day.
Sabz: Yeah man what about the ladies?
Glover: Bro first t all day, you know!
by Theycallmesabz July 10, 2008