A rat is basically the new term for "burn out" or "loser". It is someone who doesn't value hygiene or any tidiness in their lives at all for that matter. Someone who wastes their time making poor decisions like regularly engaging in illegal activity such as drug use or theft.
one dude: "damn, look at that guys hair, it's go greasy"
other dude: "What a lazy bum. I heard he cheated off some girl's chemistry test the other day"
first dude: "wow, he's a total rat"
Someone who lives a filthy life and knows a lot of shit. The rat will tell authorities about a crime, however they are not the ones committing the crimes themselves.
There’s a rat in my boot, who wants to rid their house of criminal activity.
If someone calls you a rat that means that they think your annoying,gross and messy all the time and you should take a shower
Guy 1: rat!
Guy 2: whatever dude (¬_¬)
A beautiful rat is a friend who's a rat just like me. My cousin is a fine example.
Someone in a game who uses annoying stratagies to win. Sometimes also refered to as mole rat
P1: *Kills P2 in Call Of Duty with a riot shield*
P2: Oh my god kill yourself you rat!