Respect
Everyone’s had at least one encounter with a bad driver before. Heck, maybe you were on the receiving end of a well-deserved verbal tongue-lashing from behind a car door for your reckless driving. While we don’t condone engaging with terrible drivers since you never know what sort of trouble you can get into, when this guy did, the story ended with the OP having newfound respect for his gramps.
Apparently, the guy who cut this guy off on the freeway was none other than his grandfather. When he sped up to see the guy, he discovered it was his grandfather’s middle finger in the air pointed in his direction.