I will drop in his way some obscure epistles of love.
For this uncivil rule, she shall know of it.
make a fool of him!!
What kind of woman is't?
About your years, my lord.
Of your complexion.
I will smile. I will do everything that thou wilt have me.
When Sir Toby and Sir Andrew were drunk, Malvolio tried to make them quiet in a rude way and annoyed them, consequently, Maria, Sir Toby, and Sir Andrew decided to drop a fake love letter from Olivia on a purpose to "make a fool of him".
Orsino asked Cesario about the woman that he loves, but as a woman, Cesario(Viola) loves Orsino so that she said that the age and appearance of the "woman" are really like Orsino.
Malvolio read the letter faked by Maria, Sir Toby, and Sir Andrew, and misunderstood that Olivia really likes him. The three viewers were really happy that he was tripped.