Outside-Inside Slur

Alice tells Bob (who belongs to group X, or at least claims it, or seems so): "Outside you're X, but inside, you're (really) Y!" Implying that Y is evil, or intolerant of non-Y (often the case if Y = "white"), or at best that Bob is a phony.

Comic Books

 * Top Ten has a robot deriding Joe Pi as being too human by calling him "Spambo" (metal on the outside, meat on the inside)
 * In Double Happiness, the (Chinese-American) protagonist complains that he's "such a twinkie" (yellow on the outside, white on the inside).

Film

 * In Harold and Kumar Go To White Castle, Harold (who is Asian) talks about being referred to as a twinkie—yellow outside, white inside.

Live Action TV

 * In an episode of Scrubs, Dr. Cox derides Turk for being whiter than he is.
 * On Veronica Mars, Hispanic students who excel in school are called Coconuts: brown outside, white inside.

Professional Wrestling

 * in the UWF "Iceman" King Parsons once called Savannah Jack an Oreo for teaming with Gentleman Chris Adams. (Adams had been Parsons' tag team partner until Parsons had a Face Heel Turn.) The first time I ever heard the term, which is why it stayed in my brain all these years.

Western Animation

 * There's an episode of King of the Hill where Khan's idol, Ted Wassonasong, calls him a banana (yellow skin, white inside), after which Khan tries to get in touch with his Laotian culture.
 * Inverted on American Dad. Francine, who was adopted by Chinese-American parents, stars in a show about her life where her fake mother compliments her by calling her a "reverse banana": white outside, yellow inside.
 * In the Drawn Together episode where Ling-Ling gets his "Asian eyes" fixed, Godzilla shows up and accuses him of being a "Twinkie": yellow on the outside, white on the inside.

Real Life, about races

 * "Oreo" / "coconut" (black/brown on the outside, white on the inside)
 * "Banana" / "Twinkie" (yellow on the outside, white on the inside)
 * "Egg" and "daisy" have both been used for the inverse.
 * Apple: Red on the outside, white on the inside (for Native Americans)

Real Life, about political ideologies

 * "Melons", from rightwingers for greens (green outside, red inside)
 * "Radishes", from communists for moderate leftists (red outside, white inside)
 * Rino (Republican In Name Only), Dino (Democrat In Name Only).
 * "Beefsteak" was used by Nazis to deride former socialists who they suspected of only joining the Nazis / SA / SS due to pressure: brown on the outside, red on the inside.
 * And the other way round: After World War 2, ex-Nazis joining the Austrian Socialists were called "Punschkrapferl" - outside red (or pink), inside brown.

Other

 * The giant statue of Christ recently built in Poland got some "concrete on the outside, empty on the inside" comments. (Actually, these are both bad as in Poland "concrete" is used to mean something unable/unwilling to reform, such as die-hards of the old regime.)
 * "Crunchie" is an (extremely mild and rarely serious) insult to intelligence, meaning brunette on the outside, but blonde on the inside.