Puzzles/Logic puzzles/Hats/Solution

The first man saw at most 1 blue hat in front of him, for if he saw 2 he would have said "red" (there are only 2 blue hats).

The second man saw a red hat in front of him, for if he saw a blue hat he would have said "red" (the first man saw at most 1 blue hat).

That's how the last man now knows the 2nd man saw a red hat on him.