If someone gets that irritated at you, and wants to fight to seriously injure or kill you, even if he doesn't have a weapon to start, He'll more than likely grab something nearby if possible to make it a weapon.
The one time that 3 punks attempted to rob me on the subway in Belgium, I refused, and decked one of them after they headbutted me. (Seriously, yes, one of them headbutted me....

)They fell back and started grabbing wood-backed seat coushins off of the chairs. I pulled out my knife, and we stood at a stalemate about 15 feet apart until they got off 2 stops later because other people were getting on. (Carrying a Knife may or may not have been Illegal in Belgium... I don't know... I was in the military at the time, and It was standard for me to carry one) All I know is the single old lady that was on the subway with me at the time was practically kissing me after I ran them off.. No idea what she was actually saying though.
Side note: This was also when I learned that I was not someone who simply complied with BG's and gave in, even with unfavorable odds, 1v3. My response to them when they said 'your wallet or I Kill you' was instantaneous and a non-thought. It consisted of a 4-letter word, followed by 'you'.
Key is gaining/keeping/maintaining distance from them before they start to attempt to pummel you with bare hands
Every other fight I've seen & NOT been in (only a few), all in Bars (Yes, I was younger at one point in my life, and did frequent these places... but only to meet women, I swear!

) if something in the immediate vicinity is easily grab-able and usable as a weapon (beer bottles, pool cue or pool balls anyone?) It probably will be. People seem to just love to make objects weapons. Mainly because I think that they think it gives them a better edge over the person they are planning on fighting.
As soon as they have a weapon, then it's a no brainer.