As a result of this discussion, I have been wondering whether it is in fact possible to construct a plausible theory that Shakespeare was a pirate. I think it is.
Disclaimer: What follows is an exercise in intentional biographical fallacy, and the only claim I make for the merit of this theory is that it is not, in fact, any sillier than some of the stuff I've seen seriously argued about Shakespeare. In other words, kids, rip this off for your term paper at your own peril.
1) What was Shakespeare doing between 1585 and 1592? This is a mysterious gap in what is, otherwise, a remarkably well-documented life. The natural conclusion is that he was out of England, or doing something illegal that he didn't want people to know about, or both.
2) Shakespeare clearly knows a lot about the sea and sailing. This is evident not only in the naturalistic dialogue in The Tempest, where you'd pretty much expect to see it, but in any number of incidental but surprisingly vivid references. Consider, for example, this passage from 2 Henry IV:
Wilt thou upon the high and giddy mast
Seal up the ship-boy's eyes, and rock his brains
In cradle of the rude imperious surge
And in the visitation of the winds,
Who take the ruffian billows by the top,
Curling their monstrous heads and hanging them
With deafening clamour in the slippery clouds,
That, with the hurly, death itself awakes?
What has the ship-boy on the high and giddy mast got to do with Henry IV? Well, not so much, really -- certainly not enough to warrant a digression this long. Clearly, this passage is the work of a poet so fascinated by the sea that he just can't keep it out of his writing, one who has evidently spent some time at sea and observed such a scene.
3) Even so, why does this make Shakespeare a PIRATE? Well, consider what he has to say about pirates. Searching the Shakespeare Concordance turns up about fifteen scenes with the word "pirate" or "pirates." Many of these references are brief. Some are not very complimentary: Shylock, for example, refers to "land-rats and water-rats, water-thieves and land-thieves, I mean pirates," and Lucio in Measure for Measure mentions "the sanctimonious pirate, that went to sea with the Ten Commandments, but scraped one out of the table." But consider the source: Shylock is a villain, and Lucio is full of shit.
Looking closely at what pirates actually do in Shakespeare gives us quite a different picture. Antonio in Twelfth Night gets accused of being a pirate, but he's really a nice, generous guy. Hamlet talks about being rescued by pirates, who, he says, "have dealt with me like thieves of mercy." Likewise, the pirates in Pericles rescue Marina ... well, OK, then they sell her into white slavery, but that's better than killing her, like all the fine upstanding citizens in the play want to do. Finally, there's good old Walter Whitmore and his captain in 2 Henry VI. These guys are learned ("And, like ambitious Sylla, overgorged / With gobbets of thy mother's bleeding heart"), honorable ("Never yet did base dishonour blur our name, / But with our sword we wiped away the blot; / Therefore, when merchant-like I sell revenge, / Broke be my sword, my arms torn and defaced, / And I proclaim'd a coward through the world!"), and even eloquent. Moreover, they perform the inestimable public service of ridding the world of the Duke of Suffolk, and make it clear that they are doing so for the good of the kingdom ("Now will I dam up this thy yawning mouth / For swallowing the treasure of the realm"). Shakespeare's plays, in short, are the work of a man who had considerable sympathy for pirates, and who takes pains to depict them as something other than bloodthirsty thieves. Indeed, we might almost imagine that he had a compulsion to rehabilitate pirates in the eyes of the world, because why the hell else would there be completely random pirates in Hamlet?
4) Check out the portrait. I rest my case.