well as far as i can tell Doncha is like saying Don't ya? which in turn means Don't You? which them becomes Do Not You?
now really, just what EXACTLY the fuck does "Do Not You" MEAN?!?!?!?!?!?!
thieums Then you have to add some signs, like a comma : "Do not, you"... And the rest is implicit, and can be :

"Do not, you sonhauffabitch"
"Do not, you platypus with a weak beak"
"Do not, you poor excuse for a dead recycle bin"

The general use of the "doncha" is then "do not" (do not something implicit), in a mean, mean way. The person that uses it probably thinks the worst things about you, and you are hereby allowed to slap him/her around a bit with a large trout.
what's it to you?
who go