Husband Bulge
This expression comes from the horror movie Cabin in the Woods, released in 2011. Basically, a "husband bulge" is an erection.
"Dude, zip up your fly. I can see your husband bulge!" erection
husband's bulge
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.