Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic is a crude teenage humor gag about an adolescent boy who has invented what he calls an "I.B.L.D." -- an "Improvised Boner Light Deflector." He proudly announces to his friends that he's been experiencing an unintentional erection, but thanks to his I.B.L.D., they've remained "blissfully ignorant."

When the girl asks what an I.B.L.D. actually is, the boy explains the acronym. In the final panel, she points out the obvious flaw: he's been conspicuously mashing a fantasy novel into his crotch for the last five minutes, which is anything but subtle. He desperately shouts "I.B.L.D.!" as if repeating the acronym will somehow make his improvised concealment method more effective. The comic plays on the awkwardness of adolescent attempts to handle embarrassing bodily functions with overly elaborate and ultimately transparent strategies.