A reckless impetuous irresponsible person.

synonyms: daredevil, hothead, lunatic, madcap, swashbuckler.

Dutch: snoever, waaghals
Polish: artysta, egzemplarz, ptaszek, ziółko

Cheerfully irresponsible:
— Had a harum-scarum youth.

synonyms: carefree, devil-may-care, freewheeling, happy-go-lucky, slaphappy.

Roget 458: inattentive; unobservant, unmindful, heedless, unthinking, unheeding, undiscerning^†; inadvertent; mindless, regardless, respectless^†, listless etc. (indifferent) 866; blind, deaf; bird-witted; hand over head; cursory, percursory^†; giddy-brained, scatter-brained, hare-brained; unreflective, unreflecting^†, ecervele [Fr.]; offhand; dizzy, muzzy^†, brainsick^†; giddy, giddy as a goose; wild, harum-scarum, rantipole^†, highflying; heedless, careless etc. (neglectful) 460.    inconsiderate, thoughtless.    absent, abstracted, distrait; absentminded, lost; lost in thought, wrapped in thought; rapt, in the clouds, bemused; dreaming on other things, musing on other things; preoccupied, engrossed etc. (attentive) 457; daydreaming, in a reverie etc. n.; off one's guard etc. (inexpectant) 508^†; napping; dreamy; caught napping.    disconcerted, distracted, put out etc. v.. ... show more

In a wild or reckless manner:
— Dashing harum-scarum all over the place.

synonym: pell-mell.

Roget 59: irregularly etc. adj.; by fits, by fits and snatches, by fits and starts; pellmell; higgledy-piggledy; helter-skelter, harum-scarum; in a ferment; at sixes and sevens, at cross-purposes; upside down etc. 218.    ... show more