1
general::
One can expect boys to act childishly or misbehave, as in We told the kids not to eat in the living room, but when we got home there was a big mess there? oh well, boys will be boys. This term came from a Latin proverb, translated as "Children [boys] are children [boys] and do childish things." In English it was first recorded in 1589.
American Heritage Idioms
2
general::
Phrase(s): Boys will be boys.
Prov. Boys are expected to be irresponsible or boisterous. (Also said ironically about men.) • You can’t blame David for breaking the window with his baseball. Boys will be boys. • My husband can’t resist driving eighty miles an hour in his new sports car. Boys will be boys.
McGrawhill's American Idioms And Phrasal Verbs