childish behavior
Immature and irresponsible actions between a pair of "less than grown up" lovebirds which results in da girl's soon having to start "eating for two".
In da infamous "Mary Jane" parody of da classic "hill-climbing duo" kiddie-poem, da fact dat "silly Jill forgot her pill" caused her delightful encounter wif her male companion to become downright "childish behavior"!