My friend is throwing up blood what should he do ? he has not eaten anything all day, but eggs in the morning and feels weak.

Hematemesis: throwing up blood in all but the most minor cases is a reason to go to the er. Separate issue is if someone cannot take any fluid they will eventually become dehydrated. In adults 12 hrs is generally well-tolerated BUT if someone is LOSING a lot of fluid from a LOT of volume of vomiting (rare) or diarrhea (common) then... will need fluid. Without an actual examination, I cannot give specific info