Superlative form of unfunny: most unfunny.(adjective)
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Use "unfunniest" in a sentence
"But some of the unfunniest stuff in the funny pages used to be entertaining, in a distant time and a vanished context."
"From Kelly Khuri to Ginni Thomas to Sharron Angle and Rand Paul and Ken Buck to many many others, these are some of the unfunniest people out there."
"Even during my horrible check-in experience at the Riviera; even during the darkest, unfunniest moment of Criss Angel's show; even during the resulting half-hour phone call from his show's publicist during which she insisted I'd been grossly unfair to Angel -- even during all of that, I haven't once been bored."