Point of interest, there are already seven people called Oli on the main site.
I wouldn't worry too much about name clashes. It's something that happens in real life all the time and we get along with it because we learn other identifying marks (faces, voices, etc). On Stack Exchange we have avatars.
Between the two, that should provide people with enough individuality without needing force the next Oli to call himself BigBadOli6969, just because I nabbed "Oli" first. That's the trade-off here. Silliness vs individuality.
There is another side to this: when people purposefully imitate another user by copying their avatar. In these cases I think we would take action to prevent calamitous hijinks ensuing.
But again there is a problem when people use publicly available material as their avatars. You have selected an image from a very old internet animation. You are certainly not the only person using it.
You have to expect some level of clash if you use both a common nickname and a commonly used avatar.