Old-timey, folksome, or religious nutjob's "polite" or naive way of explaining what a boner, visible underneath clothing is. It implies that the speaker doesn't believe sex or sexual desire should happen outside of marriage; so only a husband would have a boner. But "boner" or "erection" are too scandalous and obscene to say.
That guy in class was totally trying to hide his....husband's bulge under his books.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi