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!"