When Henry wakes up the morning after returning to his regiment , there is a fight among the soldiers. What is it about ?

From the text:

From one of these near came sudden sharp voices in a row. It appeared that two light-footed soldiers had been teasing a huge, bearded man, causing him to spill coffee upon his blue knees. The man had gone into a rage and had sworn comprehensively. Stung by his language, his tormentors had immediately bristled at him with a great show of resenting unjust oaths. Possibly there was going to be a fight.

The fight is caused by tension, as everyone is on edge. Something as simple as teasing in spilt coffee can easily turn into a fight in these conditions.