The Collaborative International Dictionary
ham it up
Ham \Ham\ (h[a^]m), v. i. (Theater) To act with exaggerated voice and gestures; to overact.
ham it up to act in a showy fashion or to act so as to attract attention; to ham. [Colloq.]
Wiktionary
ham it up
vb. (context idiomatic performing arts English) To deliberately exaggerate one's emotions or movements, or to overact or act badly.
WordNet
Usage examples of "ham it up".
Becker claimed Thomas Wolfe as an influence but he didn't wail and ham it up like Wolfe did.
Nothing to worry about, she's too much of a pro to ham it up in public.