wwestar you are right and wrong...nipping is just what male guppies do..that is why you are recommended to have 2 or 3 females per male guppy, so that the harrassment is spread out....they do nip so that the female will drop the fry quicker, but in most cases they don't eat them, so it is not correct to say that this is the sole reason for the nipping
EDIT: oh, and as for the males fighting...they may chase each other a little but generally speaking male livebearers are prefectly fine together int he same tank...so people even have all male tanks so that there are no fry to worry about...maybe the other male guppy died for whatever reason and the other one was eating him..
wwestar: no need to be rude about it...you shouldn't scare people so much