By using the idea that if something is inside you, you are then outside of it. Commonly used for drinking buddies when the drink is placed in front of you for enthusiastic consumption.
Alternatively chicks could use it to describe a guy they fancy getting a length from
*Returning from the bar*
"Get on the outside of that Fella!"
*watching hot bloke walking by*
"hey girlfriend, wouldn't you just like to get on the outside of that!"
It comes from the song "Ice Cream Paint Job" by D O double R.
He is talking about his car.. but what people fail to realize is that he is really talking about his girl's vagina.. vajayjay.. girl's private part.. yes..
"Dang, bro, my girls vagina.. It's cream on the inside clean on the outside!"
"Round the outside" can refer to dancing, specifically square dancing. "Country" dress and traditions have caught on in many southern states, notably Florida, Texas, and Georgia.
"Three buffalo gals go 'round the outside
'Round the outside
'Round the outside
Three buffalo gals go 'round the outside
And do-si-do your partner..."
-- Malcolm McLaren
"Two Trailer park girls go around the outside ..."
-- Marshall Mathers (a.k.a. Eminem)
used on someone who's in a bad mood and goes off the handle at friends and family over simple things....also a way of saying a woman has balls or says something with gusto; calling a woman tough and mean like a guy
note: it's quite sexist, so you might wanna consider who you use this on....make sure they have a sense of humor