Overly theatrical (10)
'overly theatrical' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for histrionic that I've seen before include "Overly theatrical" , "Of acting; dramatic" , "Melodramatic" .)
(Other definitions for operatic that I've seen before include "Irate cop (anag)" , "music drama" , "description of Lulu?" , "as in G&S?" , "Relating to musical drama" .)