on the 5 is talking about the 5 point star. It is used by gangs named the Vice Lords and Bloods. These two gangs worship the 5 point star. So indtead of sayin on my momma, they say on the 5.

when you're hungover as shit after a spending a night drunk as a skunk

Phrase similar to “on my momma.” “On the set.” On my dead homies.” used by gang memebers and afiliates in various gangs under the People Nation..such as Black P stones (BPS), Almighty Black P Stone Nation (ABPSN), Almighty Vice Lord Nation (AVLN) aka Vice Lords, Latin Kings (ALKN) Bloods under UBN (mainly northern sets on the east coast)

4 Corner Hustlers (4CH) and a few others..their main symbol that they all share is the 5 and the 5 pointed star.