A woman once said to me that being friends with a girl you fancy is creepy, because you 'creep' up on them, waiting until their guard is down, and then pounce. So I gather that the idea of being 'creepy', is pretending to be one thing, and then unexpectedly turning into something else, that others find really uncomfortable, and freaks them out. It makes people worried that they always have to on their guard with you.
I gather from your post, that doing this is your sort of thing. So yeah, what you're doing is creepy.
I would suggest that you tone it down a little. You can shock people and get away with it. But people mostly respond to tone of voice, and facial expression, not your content. They aren't freaked out by what you said. They are freaked out by how you said it so unexpectedly loudly.
You can also prevent the anxiety, by calming people down afterwards, so they are left feeling OK after, and their anticipatory recall is also that of a positive after-feeling. A good way to do this, is after you shouted your exclamation, to then smile broadly, and then laugh loudly, as if you were trying to make them laugh. This lets people know that your intent was humour, to make them laugh, and not at their expense. Sometimes, that can backfire, though, if none of them laugh with you. So it takes a little finesse, possibly adding in a phrase or two to encourage them to see the experience as humorous as well.
But if you aren't that good with the finessing, the quieter approach is easier and more reliable. Plus, the smart people will pay attention to the content, and will get it, and the stupid people won't, but will not get freaked out, and will just think you're weird.
My Mackey from South Park is weird. Mr Garrison is plain old creepy. I think between the 2, it would be better to be thought of as Mr Mackey than Mr Garrison.
just because i like to know about them too... 
