As I understand, the point of memento mori is this, given that I might die at any time of heart attack, lightning strike, etc. , how should I treat that other guy; you know, the one who just cut me off? Should I escalate the situation into road rage or would it be better to simply forgive and move along without letting the situation bother me for the remainder of my ride?

I doubt those Roman stoics ever considered bicycle road rage, but you get the point.