You and Thee
In Henry IV Part 1, in the exchange between Hotspur and Owen Glendower, about calling up devils from the vasty deep, Hotspur deliberately shifts from the word you to thee when he addresses Glendower. You was often used to convey respect while thee was used when speaking to someone of inferior rank, for example a child or servant. Hotspur used you in addressing Glendower until Glendower said, “Why, I can teach you, cousin, to command the devil.” Then Hotspur replied, “And I can teach thee, coz, to shame the devil.” This shift from you to thee (and from Glendower's cousin to Hotspur's coz) would have been particularly obvious to an Elizabethan audience.
In Twelft Night, when Sir Toby Belch encourages Sir Andrew Aguecheek to challenge in writing a competing suitor to a fight, he says, “Taunt him with the license of ink. If thou “thou”-est him some thrice, it shall not be amiss.” Here Sir Toby explicitly states that thou will be insulting. The joke is doubled because Sir Toby calls Sir Andrew thou with, “If thou ‘thou'-est him…” Again, an Elizabethan audience would have caught the joke.
This is not an inviolate rule. Sometimes thou was used as an expression of intimacy or affection. Romeo and Juliet, for example, who were of the upper classes and ought to have spoken to each other and of each other with you, almost always used thou, e.g., Juliet's “O Romeo, Romeo, wherefore art thou Romeo?” and then Romeo's, “O, speak again, bright angel, for thou art / As glorious to this night, being o'er my head, / As is a wingèd messenger of heaven.“