Here's a few off the top of my head.
Reservoir Dogs: Right after Mr. Pinks rant about tipping, Joe walks up to the table to gather up the tips. He gets to the table, looks down at a messy pile of crumpled up $1 bills, and pretty much instantly knows that it's a dollar short. Is he Rainman or something?
The Shawshank Redemption: Red throws down knowledge by telling us "I mean...how often do you really LOOK at a mans shoes?" That's true when you're face to face with someone, but Red was looking down at Andy from fifteen feet in the air and Andy was wearing mirror-like shoes. Wouldn't those shoes stick out like a sore thumb in a prison?
Rounders: Matt Damon picks Edward Norton up from prison. As they're chit-chatting and catching up in the vehicle, Matt damon suddenly notices a tattoo on Worms arm and asks him about it. Worm pulls up his sleeve, from wrist to elbow, and shows Matt Damon the tattoo which is small and halfway up his forearm. How did Matt Damon notice the tattoo in the first place when Worms shirt was covering his arm all the way to the wrist?