In Act 3, scene 1, what inference can be made as to Mercurio wanting to fight Tybalt? And what is the dramatic irony?

In the Elizabethan time period, it was thought that a man
too much in love is not actually a man at all, he is "effeminate".  In this scene, Romeo
fights with his two selves - the more manly version that Mercutio knows who would fight
at the drop of a hat and the softer version that Juliet knows who tries to keep the
peace as he does not wish to fight with his new wife's
kinsman.

There is a lot of debate on this subject, but it
can be argued that Mercutio (his name means a mercurial nature) fights Tybalt on Romeo's
behalf both to restore Romeo's manliness and because Tybalt essentially calls him bi or
gay and says he's in love with Romeo.  It can be argued that this makes Mercutio
especially angry because it's true.  The dramatic irony there would be that Mercutio
fights Tybalt so Romeo doesn't look effeminate, but it is actually (according to
Elizabethan sensibilities) Mercutio who is effeminate.