Short for "too baked didn't read". This comes from the original tldr (too long didn't read).
The original is used on the internet when commenting on a text that is too long to bother reading for the person using the phrase. Tbdr is the same, only the reason for not reading is not the length of the text, but the poster being stoned.
When commenting on something else in the post but the text:
"Tbdr, but who is the guy in the picture?"
When making an off topic comment in a post:
"Sorry, ot - tbdr. anynbody else wishing for a sandwich?"
Or simply to mark that a text is too long for the reader considering their current state:
Prices shown in USD.