Steve Martin and Martin Short are in the middle of a comedy tour called A Very Stupid Conversation. During their show Friday night at the Majestic Theater in San Antonio, David Letterman made a surprise appearance to rip on Donald Trump!

Dave said he was enjoying his retirement until Donald Trump announced he was running for president.  That's when Dave realized, "I've made the biggest mistake of my life ladies and gentleman."

Dave then did a Top 10 list of interesting facts about Trump.