This is in the episode where Drew tries to get the pot-hole repaired. At the very end, when Mimi tells her boss that his left eye looks red, and gives him some eye drops. However, he puts the drops in his right eye. (When you are watching, take into consideration that your left is their right, and vise-versa.)
Actually, he puts the drops in both eyes, the reason Mimi told Mr. Wick to put the drops in his eyes, was so that he could lean his head back, by doing so, his toupee would fall off, and hang off his head, which was a running gag in the episode.
I'm surprised that they allowed this slip up in here because it isn't really a slip up because no one will know if she was talking about Drew's Left Eye as Drew sees it or he sees it. So it really isn't a slip up because how do you know exactly how she was saying it?