When I speak of the opening to Romeo and Juliet I tend to jump right into the entrance of the Montagues, and the subsequent thumb biting. The opening lines to me have always been simple word play intended to do little more than calm the audience down and let them know the play's starting. I get that they are punning off of each other, and if it's a competition, it seems like Gregory wins (the person who goes second in such a contest usually does).
So, what is "carry coals" supposed to mean, and why is it important for Sampson to say it? It sounds roughly like "We're nobody's bitches", pardon my language. But that's what it sounds like, like some young kid strutting around with nobody to bully so he tells his friend "Hey, we don't take no crap from no one," like his friend needs to be told that.
Well, then we'd be colliers - but what's that mean?
"If we be in choler we'll draw" seems straightforward enough -- piss me off (choler==anger), and I'll draw my sword.
"Draw your neck out of the collar" -- keep out of trouble, stay out of the hangman's noose / guillotine? Would such a reference be accurate for Shakespeare, or is that a miss?
"I strike quickly, being moved." - Sampson gives up on the punning there, apparently, and starts over with more of the "I don't take crap from nobody" stuff.
Gregory plays up on the passive voice - "But thou art not quickly moved to strike" sounds suspiciously like "You're too chicken to take the first swing."
"A dog of the house of Montague moves me" -- (thanks for the Montague reference!)
"To move is to stir, to be valiant is to stand, therefore if thou art moved, thou runn'st away" - does anybody else get the feeling that Gregory is not evenly matched in this battle of wits?
... and then it gets into the whole "maidenhead" discussion. I could keep going but there seems a good place to break. I'm mostly curious about those first two lines (and, well, whether I've grossly misinterpreted any of the others).