He was best known for his frequent guest appearances on Jack Paar's shows of the late 1950s and early 1960s. On one such appearance, when Douglas was well established as a Paar guest, he was chastised by Paar for holding a stack of file cards with his jokes while talking with Paar. When Paar returned to television in 1973 and was confronted by unexpected low ratings, he engaged Douglas to contribute monologue material by mail. One week there was no mail from Douglas; but his next package contained a note: "Sorry I didn't send anything last week. I forgot you were on."