What to do in a fight?

I live in the type of place where theres hooligans and wannabe hooligans. They dress, talk, walk and act exactly the same the only difference is one axtually has the bullocks to get into a hard fight. There are probably more wannabe thugs, but how do i know if the lad whose actin smart and nudgin me a bit is the real deal....cuz if hE is im SCREWED. Im not actually going to do this but if i pulled out a nife what do you think would be the most likely thingmthe other guy would do in the case of a. Fight?