In a hammy manner; with exaggerated or theatrical behavior or acting.
From hammy + -ly (adverbial suffix). Created in standard English in the 20th century as 'hammy' became established enough to require an adverbial form.
Adding -ly to create adverbs is one of English's most productive word-building strategies, and 'hammily' shows how even slang terms from theater can rapidly generate their own grammatical families once they gain cultural traction.
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