It just says "spend a hero point to reroll a check". If some bruiser just crit me, could I force him to make a reroll?
The way it reads and the way hero points are thematically used, no. You don't roll his attack, so you cant choose to reroll it either.
A hero point is a moment of heroics for your character. Its not very heroic of the character if the enemy swings at them. Because whatever was originally rolled no longer exists it would just be a enemy swinging at them one time with the hero doing nothing.
Also in the rules it says you can spend the hero point on behalf of your companion or familiar, but not on a enemy.
Of course this is up to interpretation until we get a eratta. I can see where your coming from though. PG 467 under describing heroic deeds lead more into the thematic's of it. Where your supposed to describe the heroic deed you did when spending that hero point. Since your rerolling a d20 and not changing your own defenses you cant describe how what you did heroically to change their attack (not without it just sounding like a AC change. Even a epic parry or blind luck would be changing your stats, not the enemies since its your heroic deed.