McCain called Cindy a "cunt" in front of 3 reporters in 1992:

Three reporters from Arizona, on the condition of anonymity, also let me in on another incident involving McCain's intemperateness. In his 1992 Senate bid, McCain was joined on the campaign trail by his wife, Cindy, as well as campaign aide Doug Cole and consultant Wes Gullett. At one point, Cindy playfully twirled McCain's hair and said, "You're getting a little thin up there." McCain's face reddened, and he responded, "At least I don't plaster on the makeup like a trollop, you cunt." McCain's excuse was that it had been a long day. If elected president of the United States, McCain would have many long days.

Cindy's fortune comes from her father's beer distributorship, which had many ties to the mob.

Which may be why McCain refused to release Cindy's 2006 and 2007 tax returns.

Back in 2004, then-Republican National Committee chairman Ed Gillespie excoriated John Kerry in the media as a result of the presumptive Democratic nominee's similar decision not to publicly release information on his wife's substantial assets -- so we can assume that he will hit McCain for doing the same thing this year, right? I'm not holding my breath. In fact, Heinz Kerry did release a portion of her 2003 returns during the 2004 campaign.)

The partial release of Cindy's tax returns could be hiding something very important:

These media reports, therefore, have advanced the McCain campaign's comparison between Cindy McCain's limited release of financial information and Heinz Kerry's, and in doing so, ignored a key distinction in the information they released: Unlike Heinz Kerry, Cindy McCain did not release sufficient information for the public to determine the extent to which she benefited from the tax cuts her husband supports extending.

Slate writes:

Aside from a Wachovia checking account, in which he keeps between $15,000 and $50,000 (wouldn't some of that money earn more interest in a certificate of deposit?), all of the couple's assets are in Cindy's name. John McCain's tax return is so anemic, so marginal to the couple's actual financial situation, that he doesn't even take a deduction for interest on his home mortgage. Presumably Cindy does, since disclosure forms indicate that she has several mortgages.

We don't know for certain whether she does, because the campaign has declined to release Cindy McCain's tax returns. This data gap sets McCain apart from his Democratic opponents, who have released jointly filed tax records going back a minimum of seven years. Thanks to McCain's lack of genuine opposition in recent months, there has been very little clamor to release Cindy McCain's returns, even from those Republicans who loudly insisted that Hillary and Bill Clinton were hiding something in theirs. 

Cindy says she will never release her tax returns, even if she becomes First Lady!