The phrase “is that my bestie in a tessie?” is a playful and affectionate way to ask if someone is your best friend. It is often used in a teasing or joking manner, and it can be a way to show your closeness to someone.
The phrase is thought to have originated in the early 2000s, and it quickly became popular among teenagers and young adults. It is still commonly used today, and it has been featured in popular culture, such as in the movie “Mean Girls.” There is no definitive answer to the question of what a “tessie” is, but it is generally thought to be a term of endearment for a close friend.