All of the secret awards which involve flipping at some point or another can generally be obtained by holding both flippers up at the appropriate moment. Flipping vigorously may or may not work. Doing this at several points in the game will lead to Secret Awards, which probably aren't worth many (or any) points, but are extremely amusing and tend to impress crowds even long after you've grown tired of them.
Holding the flippers as the Snackbar opens awards 'NO MORE BAD FOOD' and blows up the Snackbar. It is rumoured that this tends to make the awards from the Snackbar more pleasant (less likely to be food). Note that you have to hold the flippers before the lights come on in the animation and the sign says OPEN.
Holding the flippers as the Snackbar attendant gives you a menu item will earn the quote 'Come here, punk', while a hand reaches out and chokes the attendant, labeled 'Choking Fatality'. This choking goes on for quite a while after the animation ends - listen closely.
Flipping at the end of Video Mode, when your opponent is dazed and the display says KNOCKOUT, will knock his head completely from his body (which is rather gruesome), and is labeled 'FATALITY'. 'There's more where that came from!'.
A ball which goes around the Back Orbit of the game when it has not been shot from the plunger awards the Sneak-In Bonus, which is 1M the first time, 2M the second, and so on. A very fast shot up the Center Shot is the best way to try to get this. It's easy on some machines. The ball then comes screaming down the Left Saucer Lane. Unfortunately, it's usually preferable to have the ball stay in the P-A-I-D Lanes instead.
When you reach 35M in Super Creature Feature, the game stops awarding points, and the display says DON'T BE GREEDY. Presumably this is to stop 'Diner'-style play from keeping the ball going in the Whirlpool forever. It's actually quite hilarious.