Ah, O'Reilly, a man that in his stupidity is greatly lucky in having NOT been featured as one of the past twelve Malicious Morons, that given all his humongous amounts of imbecility. Fundamentally speaking, the single-handedly most loathed thing about him personally is how he THINKS that he is a 100 % "non-biased" news source, and is far too keen on self-professing it all the time, too. The man is first of all on Fox News - a news network uniformly defined by its massive proliferation of misleading information and massive inaccuracies - and his constant passive-aggressive swipes at liberals and proud conservative patronage make transparent his right-wing bias everyday. (The photo to your right depicts him hanging out with Ann Coulter, a rabid conservative whose own malice earned herself the entitlement as a past month's Malicious Moron, too!)
However, during his excesses of overdramatized, conservative breakdowns, Bill O'Reilly has made himself easily caught showing very emphatic biases & uneducated perspectives. These few mortifying examples below, not any single itself necessarily being called his WORST, are all highly collective highlights in O'Reilly's style of malicious stupidity:
1. This so easily demonstrates O'Reilly's incompetence to be a non-biased, credible political reporter due to his lack of elementary knowledge about one of America's most recognizable constitutional amendments. In this following quote, contextually speaking, O'Reilly is defending the illegal torture tactics of the Bush Administration: "Look, if it were illegal, Bush and Cheney would have been arrested. You’re sitting authorities, the attorney general ruled waterboarding was not torture. It was legal. Rare occasion it was used." Um, excuse me, but the Eighth Amendment to the American constitution prohibits cruel and unusual punishments, and there's the Feds were finally held under fire for the atrocious inhumanities taking place. (Does this single quote not prove the statement that he is a moron a total truth, not an opinion?!)
2. This one is so stupid that I MUST provide you a video to see it being in said. A caller from Canada noted to O'Reilly that the Canadian life expectancy rate is higher than America's in response to O'Reilly's harsh criticism of Canadian Health Care. This was his brainless response, quoted and videoed by The Huffington Post: 
O'Reilly: "Well Peter, that's to be expected," he said, "we have ten times as many people as you do!"
"The 'shut up' line has happened only once in six years." – responding to a viewer who said if he was so concerned about public figures being bad role models for children, he should stop interrupting guests and telling them to shut up, Nov. 15, 2002
3. "If I'm the president of the United States, I walk right into Union Square, I set up my little presidential podium, and I say, 'Listen, citizens of San Francisco, if you vote against military recruiting, you're not going to get another nickel in federal funds. Fine. You want to be your own country? Go right ahead. And if Al Qaeda comes in here and blows you up, we're not going to do anything about it. We're going to say, look, every other place in America is off limits to you, except San Francisco. You want to blow up the Coit Tower? Go ahead.'" - after San Francisco voted to ban military recruiters from city schools, Nov. 8, 2005
4. "I just wish Katrina had only hit the United Nations building, nothing else, just had flooded them out, and I wouldn't have rescued them." - on his radio show, Sept. 14, 2005
5. As videoed and reported here, this quote well emphasizes O'Reilly's consistently degrading view of gays, speaking of them like they are a less human, outlandish demographic. This is what he thinks of a French McDonald's commercial which happens to feature a gay young male: “...straight people are going to watch that too”, but that McDonald’s is entitled to make a “political statement.” When Skinner said that the ad was meant to show how McDonald’s appeals to a diverse group, O’Reilly asked "Do they have an al-Qaida ad?" he asked. "You know, 'Come as you are' — boom." HOW.DARE.HE. Seriously?! Him even trying to label it a 'political statement' in a country like France is fruitless and stupid - gay people are just equal people like everyone else .
6. Now in direct context, let's take a look at a short clip demonstrating his disrespect for the first amendment - his hatred for Atheists, a constant underlying bias exemplified: (This also happens to include of one our more hated Malicious Morons once again, Anne Cunter - er, *coughs* Coulter that is.)
There you have it, ladies and gentlemen. I would say just watch his show on any given day for more concrete evidence of his moronic behavior, but I don't want any responders to my site to sue me later in civil damages for causing the likeliest result of watching: a grandiosity of unintelligible, emotionally distressing lies.