Random, humorous, what's not to like?
As most people on the internet are aware, randomness is a widely accepted component in most forms of humour nowadays.
This flash is no exception.
Using the scenario of a presumably senile old man harassing a store clerk is not the most original choice, but it works because of your fast pacing of the plot.
Jumping from one incoherent sentence to another and retaining the humour is something that takes skill, and fortunately for you that isn't a problem.
The animation required to convey your story was minimal, but the animation in this flash was smooth and clean. No hiccups as far as I could tell.
Voice acting was important for this flash, since it relied on the ramblings of an ld man, and a confused clerk. These are hard voices to convey, but you had me convinced.
Though it could have developed into something more (have McDouche berate random people on the street instead of a store clerk would have in my opinion, aided the general direction of the story) I believe you did an admirable job on this flash.