Oxford Dictionary
slap-happy
slap-happy ▶adjective informal 1 cheerfully casual, often in a careless or irresponsible way: he possessed sauntering slap-happy courage. • (of an action or operation ) unmethodical; poorly thought out: slap-happy surveying methods. 2 chiefly N. Amer. dazed or stupefied from happiness or relief: she's a bit slap-happy after such a narrow escape.
Oxford Thesaurus
slap-happy
slap-happy adverb informal 1 Drysdale's slap-happy friend: happy-go-lucky, devil-may-care, carefree, cheerful, breezy, easy-going, nonchalant, insouciant, blithe, airy, casual, irresponsible. ANTONYMS serious, solemn. 2 the slap-happy way the tests were carried out. See slapdash. 3 she's a bit slap-happy after such a narrow escape: dazed, stupefied, punch-drunk, unsteady, wobbly.
Sanseido Wisdom Dictionary
slap-happy
sl á p-h à ppy sl á p h à ppy 形容詞 ⦅くだけて ⦆1 ⦅英 ⦆(陽気で )不注意な, 無責任な (slapdash ).2 (妙に )上機嫌な, 楽天的な .3 (パンチを食って )ふらふらの .