Wayne Brady says he takes "full responsibility" for using Trig Palin and his Down Syndrome as a punchline at the "Comedy Central Roast of Roseanne" ... insisting "no malice or harm was meant."

Brady has been taking some serious heat for the past week ... over a joke in which he says Sarah Palin hates Jeff Ross because he reminds her of "what Trig is going to look like when he's 40."