"insouciant" in the adjective sense
1. casual, insouciant, nonchalant
marked by blithe unconcern
"an ability to interest casual students"
"showed a casual disregard for cold weather"
"an utterly insouciant financial policy"
"an elegantly insouciant manner"
"drove his car with nonchalant abandon"
"was polite in a teasing nonchalant manner"
Source: WordNet® (An amazing lexical database of English)
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