It's cliche, but it's become one because it's such a strong narrative device. Screwdrivers are cliche, but they don't stop being useful. Like screwdrivers, this narrative tool is not perfect for every job - but when it's the right thing, and you use it properly, it's the best tool for the job.
It's probably most often used in situation comedy (one might argue that the entire genre is built around "it's not how it looks" situations), but it can be done in a lot of different ways. A lot of murder mysteries hinge around scenes like that; for instance, the wrong person finds the body and is immediately discovered standing over it. "Oh no! He's killed Mr. Body!" the maid shouts. "No!" shouts Professor Plum, "It's not what it looks like! I was just looking for the trash can!" "So you can dump the body?! Someone grab him before he gets away!" (And of course, the innocent man runs away, thereby proving his guilt... mystery ensues.)
Your challenge this week is to write such a scene. Try to give the characters very credible reasons to be in whatever easily-misunderstood circumstance they're in, and don't be afraid of the cliche - this sort of thing happens all the time in real life. And no, you don't have to have someone say, "It's not what it looks like!"
So get to it. Keep it under 800 words or so and come on back here on Sunday for the linkup.