Basic Trope: A character manages to hide his identity with a disguise that shouldn't have fooled anyone.
Straight: Bob wants to spy on Dave, the Corrupt Corporate Executive. Although they know each other well, once Bob puts on a pair of sunglasses and a suit, Dave doesn't recognize him and tells Bob his plan.
Dave doesn't recognize Bob because he's carrying a briefcase.
Bob puts on his sunglasses and suit and no-one recognizes him.
Dave can identify everyone else on the planet (including the people he never met) even if they had put on elaborate disguises. Of course, the only one he can't identify is Bob, even without a disguise himself.
Bob messes up his hair a bit. No one recognizes him.
Downplayed: Dave is somewhat suspicious of the disguise, but ultimately decides he's being paranoid.
Dave is blind, so Bob's disguising his voice is enough.
Dave has only met Bob in person once.
Dave is The Ditz. Anyone else would see through the disguise, but Dave is just too stupid.
Bob is a very good actor, so a simple change in clothing, accompanied by a change in mannerisms, can make him seem like a totally different person.
Deconstructed: Bob comes from an extremely superficial society in which people recognize one another not by any fundamental traits but by surface physical appearance. The author uses the success of Bob's ridiculous "disguise" to comment on human superficiality.
Reconstructed: If someone were to over figure out his identity, or Bob were to tell someone his identity, it will inspire a new wave of free thought and creativity.