Movie and television script cliche

Here's another quickie.
Both movies and television shows are guilty of this. Did you ever notice on any given movie or television show, when someone gets caught kissing or doing the nasty with someone who they are not supposed to be doing those things with, the first thing out of the violator's mouth 9 times out of 10 is "It's not what you think,"? REALLY? So, you weren't playing tonsil hockey with my best friend from high school? So, you weren't drilling our neighbor on the kitchen counter? This kinda spits on the minds of the viewer too. Are script writes so tapped for ideas that they have nothing else for their characters to react with except this old standby? I would love to see a movie where someone gets caught and reacts with: "Yes! This is exactly what you think it is! Surprise! Remember Stephanie? I am doing her in our garage on my workbench with Kenny G playing. I always listen to Kenny G while I am out here!" But that is just me.