like hell vs like fun

like hell and like fun both are adverbs.

Word	Noun	Adjective	Verb	Adverb
like hell	No	No	No	Yes
like fun	No	No	No	Yes

As adverbs, like hell and like fun are synonyms defined as:

like hell and like fun: used ironically to indicate the opposite of what is stated

like hell (adverb)	like fun (adverb)
(informal) with great speed or effort or intensity; used for emphasis	used ironically to indicate the opposite of what is stated
used ironically to indicate the opposite of what is stated