First, girls need time and money:
Girl = Time * Money
And we know that time is money:
Girl = Money * Money
We also know that money is the root of all evil:
Money = Evil ^ 1/2
Money ^ 2 = Evil
So we are forced to conclude that:
Girl = Evil
time = money
girls = money x money = 'money' squared
money = 'the root of all evil'
girls = (square root of evil) squared
girls = evil
guy 2: yep, they're evil
guy 3: you're just bitter cuz you haven't been laid in a while...