What is like 3 6 in the g6 song?

It means 3 sixes (6 6 6). I think you can figure what's going on there.

^ whoever said that has no idea what they're saying. The line is " Sippin sizzurp in my ride, like Three 6"

It's a reference to a Three 6 Mafia song called "Sippin' on Some Sizzurp"

So it means they're sipping on sizzurp like Three 6 Mafia.

^ whoever wrote this also has no idea what they're saying. Three 6 Mafia's name is a reference to 3 sixes (6 6 6). In fact, they used to go by the name Triple Six Mafia. So yes, Far East Movement was referencing the Three 6 Mafia song, but by stating their name, they are saying 3 sixes. Whether they realize it or not, is anyone's guess. I doubt it though; they seem like pretty dumb people.