To be in someone else's territory/business. Often used to express being in over your head or being over helmed as a result of being to nosy or just being at the wrong place at the wrongtime.
*Pull out gun* "Your in big mamas kitchen now" said sam to paul as he shot him
When some draws a line and another crosses it so bad they go so far south, they end up in a city hundreds of mile away from said line, thus showing themselves to be an ass.
Steve and Joe live in Canada.
Steve: Dude I have turkey fingers.
Joe: What's that?
Steve: Been cooking turkey all day and my fingers have turkey grease all over them.
Joe: Well then I must have greasy mom fingers. I've been cookin your moms baby box with my fat fingers all day and now they're all greasy and smelly.