Hubris, or the idea that humans can out-cheat and be better than the Gods, is perhaps best discussed in the character of Friar Lawrence in this play. One of the major themes within this play is destiny and how is something is meant to happen, you cannot change it. Destiny is clearly against the union of Romeo and Juliet: they are called "star cross'd lovers" and numerous quotes make reference to the attempts of the lovers to defy the power of destiny ("I defy you stars" for example).
Arguably, the hubris of Friar Lawrence is what resulted in their deaths. He feels that he can marry two teens from warring houses without the knowledge of their parents. One of his reasons for doing this is that he feels this will heal the breach between the two houses of Capulet and Montague. He does not stop to think that this secret marriage might actually make things worse.
It is he who creates the scheme to re-unite the lovers, giving Juliet the potion to make her appear dead. He then sends Friar John to give this vitally important message to Romeo, not thinking what might happen if the grief-stricken and slightly irrational Romeo were not to receive it. Of course, we know that he does not get the message in time. Lastly, we see Friar Lawrence offering Juliet the chance to hide away in a nunnery for the rest of her days when he realises how terribly wrong his plan has turned out. Another example of Friar Lawrence's arrogance in thinking that he can outwit fate.