When you realize that you've been cheated on, you tend to make a lot sounds. For example: grr, argh, and ugh come to mind. Another sound you might hear yourself making is the F sound.
Now, we're not here for the lowbrow jokes, gang. We'll leave that to the sitcom writers. Of course, the F word—that queen mother of swears—is probably an appropriate reaction to realizing that your beloved has been stepping out on you. Still, why else might that choice be so effective?
We think it has something to do with the letter F. Try the F sound out loud for a minute. Hear that compressed breath exploding through your front teeth? It's like the very sonic epitome of frustration (and is it a coincidence that "frustrated" starts with F?). Shakespeare sure thought so, anyway. Why else would he pack so many F words into this little poem? We get lines like:
Why of eyes' falsehood hast thou forgèd hooks, (7)
To put fair truth upon so foul a face? (12).
This repeated beginning consonant sound is called alliteration, and, sure, there are other examples of this technique in the poem. None of those uses, however, have the impact of all those F words (clean ones, even!), driving home the speaker's disappointment as he spits out his words to fitfully flail against his fickle fate.