Saw the headline and immediately assumed they’d go straight for Malvolio’s “C’s, U’s and T’s” joke. But no! They go for the F bombs.
Actually, I never really thought of it. We all know that Shakespeare could be filthy when he wanted to, but how often did he go for the F word? The examples that they give in the article (“what is the focative case? I’ll firk him!”) had never really stood out to me.
Cracked.com, while intermittently amusing, is not a reliable source. They're incorrect about the meaning of "firk," which, while related to the modern f-word, is not synonymous with it. It means to strike or beat. So Pistol "fur him, firk him, and ferret him" threat, while perhaps suggestive, isn't explicitly sexual in nature.
The joke from Merry Wives is totally intentional, though. The whole Latin lesson scene is a pile of dirty jokes derived from Sir Hugh's Welsh accent and Mistress Quickly's dirty mind. Between them, they turn the most innocent Latin declensions into a minefield of innuendo.