You know you've played too much mortal kombat when your usual, friendly, "hey!" becomes a terrifyingly growly "GET OVER HERE!"
You know you've played to much deus ex HR when you try to activate pheromones in an argument.
You know you've played too much space marine when you run down the street at 4:00 am without a shirt, twig held high, screaming "Smash da space mehreens!"
Or maybe that's just too much alcohol.