What does romeo remind mercutio and Tybalt about in lines 86-87 of Act III Scene I of Romeo and Juliet?

I think this is the speech you are talking about:

"Alas, poor Romeo, he is already dead, stabbed with a white wench's black eye, run through the ear with a love-song, the very pin of his heart cleft with the blind bow-boy's butt-shaft. And is he a man to encounter Tybalt?"

First of all, you must understand the traditional image of Cupid, the love-god, who flies around blind shooting arrows into people to make them fall in love. This traditional image acknowledges that love can be painful. Mercutio is alluding to this when he talks about the blind bow-boy, and his butt-shaft is his arrow. But this is Mercutio, right? He isn't happy with just the image of Cupid's dart piercing Romeo's heart, he also talks about love-songs stabbing him in the ear and being stabbed by the look of a beautiful woman. all this is to say that Romeo is so absorbed in his love that he takes no time to get involved in a good fight.