Friar Laurence is talking to Romeo. By this point, Tybault is dead and Romeo has been banished. Romeo is making rash claims and unreasonable demands to get to Juliet and defy her parents. The Friar is trying to shock him with devastating insults. He cries: "Hold thy desperate hand. / Art thou a man? Thy form cries out thou art. / Thy tears are womanish, thy wild acts denote / The unreasonable fury of a beast. Unseemly woman in a seeming man. And ill-beseeming beast in seeming both!"
The friar is first challenging Romeo's physical manhood. He says he looks like a man, ("thy form cries thou art"), but Romeo is acting like a woman (a supreme insult), full of emotion and unguided by reason. To further bring it home, the Friar upgrades his insults, saying essentially, no, you are even worse than a woman. You're acting like an animal, ruled only by your appetites."