It's present on the Urban Dictionary (my usual reference for that sort of stuff.)

1. teal deer
A bastardization of "tl;dr", which is a bastardization of "Too long ; Didn't read." Usually presented in the form of a photochopped (sic) image of a deer.
Thread starter: lengthy chat log
Reply to thread: said image of a deer

Just thought I'd mention this amazing site if you weren't familiar with it. ^^