1. "Breakfast of champions." When the expression is known better than the source is, it leads morons to utter it about eating Doritos or pizza in the morning without knowing or caring where it comes from.
2. "Your tax dollars at work." Your brain cells are not at work though.
3. "If I had a nickel." If I had a hammer every time I heard someone say that, I would likely be in jail by now.
4. "Which begs the question." This has been misused so much that its misuse has become accepted usage. Even if the saying has backed its way into the realm of grammatical correctness, it still sounds moronically pretentious.
5. "___ o'clock." Beer o'clock, sex o'clock, nap o'clock, snack o'clock. How about shut the eff up o'clock?