What is the dramatic irony in A Midsummer Night's Dream?

One good example happens in Act 3, sc ii, when Helena gets angry at Lysander, Demetrius and Hermia for making fun of her. The ironic thing is, they are under the influence of the love potion and have no control over what they are doing. In fact, she isn't being mocked at all.

And, of course, the whole 'head of an ass' joke on Bottom is dramatic irony because he doesn't KNOW that he has the head of an ass...which makes his lines: "I see their knavery. This is to make an ass of me, to / fright me, if they could" (3.1.16) ...even funnier.