Cut Himself Shaving/Playing With

Basic Trope: A character lies to explain away suspicious injuries.
 * Straight: Bob has injuries from a brutal fight. When asked about his bruises, Bob lies that and says that he got them in a game of football that got rough.
 * Exaggerated:
 * Bob gets his arm chopped off. Bob explains it away as him severing it himself during a fencing lesson.
 * Bob gets severely beaten and explains that he fell down three stories of stairs.
 * Downplayed: Bob has a small bruise on his arm from being hit and explains it by saying that he hit it on a counter top when asked.
 * Justified:
 * A character was in a place or does something that they want nobody else to know about, so anything that may be relating to the secret is brushed off. May be done more carefully to avoid being mistaken as the above justification.
 * Inverted: Bob tells everyone that he was beaten up, but everyone assumes that he got his injuries in a particularly rough game of football.
 * Subverted: Bob really did injure himself playing football, but everyone thinks someone beat him.
 * Double Subverted: It turns out someone did beat him; the beating just isn't the cause of that particular bruise.
 * Parodied: Bob just beat up a gang of bikers. When asked about his battle scar the next day, he explains that the he stepped on a cat's tail.
 * Zig Zagged: Bob shows up with bruises that he explains away as being from a game of football. It turns out that this would be correct, but someone did beat him, but not where it would show.
 * Averted:
 * Bob is truthful about the origins of his injuries.
 * Bob doesn't get injured at all.
 * Bob and another person openly fight each other, not necessarily from animosity, and he openly admits that his opponent gave him the bruises.
 * Enforced: "We don't want to deal with Bob's assailant yet, so let's have Bob lie to cover up the injuries."
 * Lampshaded: "Bob sure gets hurt a lot. I mean, he plays football, yeah, but still..."
 * Exploited: Because of Bob's lies, the police never gets wind about who did it.
 * Defied: Bob never appears with any suspicious injuries.
 * Discussed: ???
 * Conversed: ???

What I'd like to know is, how on earth did you cut yourself shaving while going back to the main tropes?