A "Thou" is a gram a marijuana, stemming from the words "a thousand." A Thousand can be said as a "G". In the drug culture a "G" is a gram.
"Hey Dude, wanna hang out later?"
"Oh yea for sure dude, i think i'm gonna pick up a thou or two real quick and after that wanna hit Medusa, she'll get us stoned!"
To address someone by the second person pronoun “thou”. Back when this term was first used, it would often have been said in contempt as Thou was seen as an informal and potentially rude form of address. However nowadays, since Thou is considered by many to be more formal and respectful than the ordinary sounding “you”, it can have the exact opposite meaning and be taken as a great honor.
Historical usage: “Do not thou me, peasant, else I shall give thee a taste of this steel blade!”