WHERE DO YOU GO?

a man picks up his girl and when tellin' her he's got a plan for them both to go to a tropical location the younger brother (who had a deep metal retardation) of the man appears from the back-seat and asks:
-where are we going? I just could not hear back there.
-sorry, my dear- says the guy to his girl- I'll take you to your house, then I will head mine and when my brother is asleep I'll come back, pick you up and we shall continue what we started, right?
so, the guy delivers the girl to her own house, then go his, puts his brother in bed and when he thinks that the other one is already asleep, walks quietly towards the door and when he's already coming out he hears:
-where do you go?
the elder bites himself to disimulate his frustration and calmly replies:
-I'm going to the kitchen to get me a glass of water.
-I'm going with you.
they both go to the kitchen, drink the water and return, a long while later the guy tries to step out noiselessly again and hear:
-where do you go?
-I'm going to take a pee.
-I'm going with you
they head to the bathroom, they pee and return
A very long while later the elder one is tryin' to leave again and hears
-where do you go?
he can't disimulate his anger anymore and yells:
-I'm going to find a big black man to fuck me hard.
-what time are you returnin'?