The people on the waterfront are irresponsibly subjecting their children to unacceptable conditions.
I believe in treating the taxpayer's money as somebody else's money and it's not our right to spend it irresponsibly.
1640s, "not legally answerable for conduct or actions," from assimilated form of in- (1) "not, opposite of" + responsible. Meaning "not acting with a sense of responsibility" is from 1680s. Related: Irresponsibly.