jest at is a verb meaning "subject to laughter or ridicule". It carries one recorded sense.
subject to laughter or ridicule
“The satirists ridiculed the plans for a new opera house”
“The students poked fun at the inexperienced teacher”
“His former students roasted the professor at his 60th birthday”
Definitions, synonyms and semantic relations for jest at come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.