Wayne Brady -- BOOED for Trig Palin Joke at Roseanne Roast

File this under "Things You Didn't Expect to Hear Today" -- Wayne Brady is under fire for a RACY joke he made at the "Comedy Central Roast of Roseanne" .... WAYNE BRADY!!!

So what subject was so touchy that the crowd actually booed?? Brady made a joke featuring Sarah Palin's son Trig ... who suffers from Down Syndrome.

Now for the joke ... which Brady made while addressing Jeff Ross:

"Now the thing is Jeff ... these are all jokes, and I really like you. I really, really like you. But a lot of people hate you, especially Sarah Palin because you remind her of what Trig is going to look like when he’s 40."