/ ˌmɪsˈspend; NAmE / verb
( mis·spent , mis·spent / -ˈspent; NAmE /) [ vn ] [ usually passive ] to spend time or money in a careless rather than a useful way
SYN waste :
He joked that being good at cards was the sign of a misspent youth (= having wasted his time when he was young) .