From Longman Dictionary of Contemporary Englishhammyham‧my /ˈhæmi/ adjective if a performance by an actor is hammy, it is done with too much false emotion
Examples from the Corpus
hammy• There is some hammy acting, but the film gives an interesting insight into the gangster scene of the Sixties.• The film, although hammy in places, will certainly stimulate interest in engineering among school leavers.• Now, in the television ads, he cheerfully delivered some hammy lines before falling backwards into a swimming pool.• Christopher Plummer is great too as a hammy, Shakespeare-spouting Klingon warlord. 