harum-scarum
pell-mell
in a wild or reckless manner
dashing harum-scarum all over the place
running pell-mell up the stairs
carefree
devil-may-care
freewheeling
happy-go-lucky
slaphappy
cheerfully irresponsible
carefree with his money
freewheeling urban youths
had a harum-scarum youth
daredevil
madcap
hothead
swashbuckler
lunatic
a reckless impetuous irresponsible person