Overacting (also referred to as hamming or mugging) refers to acting that is exaggerated and overblown, usually in the pejorative sense. There are numerous theatrical euphemisms for overacting. "Chewing the scenery" or "scenery chewing" refers to extreme overacting, with the purpose or effect of dominating other performers at the expense of the production. A "ham" refers to an unskilled actor who resorts to overacting, and thus overacting can be called "hamming".
Intentional
Some roles require overly-exaggerated character acting, particularly those in comedy films. For example, the breakthrough roles for Jim Carrey (in Ace Ventura: Pet Detective and The Mask) saw him portray the lead characters in a very flamboyant fashion, as the script demanded. This has led to his being classed as an "overactor", even though he has played several "straight" roles since.
Overacting may be used to portray an outlandish character, or to stress the evil characteristics of a villain. Academy Award nominee Gary Oldman was almost immediately typecast as a criminal in his film career, and the necessity to express villainous characters in an overtly physical manner led to the cultivation of his 'big' acting style, which hearkened back to his classical theatre training and would become his trademark. This encompassed "playing everything" via layered performances that vividly express each character's emotions and internal conflicts. Oldman has conceded that he often overacts on screen, and said: "[I]t's my influence on those roles that probably they feel bigger than life and a little over-the-top. I mean, I do go for it a bit as an actor, I must admit."
Oldman's co-star in The Dark Knight, Heath Ledger, received an Academy Award for Best Supporting Actor for his portrayal of The Joker. It was hailed as one of the best performances of the decade, with some fans claiming it was 'realistic' and 'scary'. Nonetheless, the choices he made with his facial expressions, speech patterns, and mannerism - including his repeated licking and making noises with his lips, frantic arm movements, and the way in which he walks - are all over-theatrical and, in fact, common for action movie villains (for example, Agent Smith in The Matrix, Hans Gruber in Die Hard, and all the villains in the original Spider-Man trilogy) as well as for some anti-heroes, such as Alex DeLarge in A Clockwork Orange - a character Ledger said inspired him during filming - and Beetlejuice - a character whose appearance resembles The Joker's.