The present participle of 'cheek'; to behave cheekily or to talk back disrespectfully (mainly British).
From 'cheek' (used as a verb meaning to be cheeky or disrespectful) + '-ing' gerund/present participle suffix. The use of 'cheek' as a verb is primarily British and developed from the noun.
In British English, 'Don't cheek me!' is something a parent might say to a child who's being disrespectful, but this verb use is rare in American English—it's a perfect example of how the same words branch into different verbs and meanings across English-speaking regions!
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