Here is the problem:
I actively try and avoid people as much as possible when walking
And here is the solution:
If you walk with purpose (not fast, not slow, just with confidence and purpose) I find most people try not to walk into you as they realise you probably won't avoid them.
Essentially, be more Alpha
If there's someone who's clearly not going to avoid you/stop, then continue on your trajectory until the moment before impact, then stop dead.
Chances are, they'll end up walking into you (a stationary object) and feel like a right idiot. At which point they'll probably mutter something like "sorry I didn't see you".
Now, this next step is critical: it is imperative that your response to this is as condescending and sarcastic as possible; replying "it's ok", or "don't worry about it" is simply not acceptable, at the very least you should respond with something along the lines of "well clearly - only a complete ****ing moron would purposefully walk into a stationary object!
".
Of course, taking this approach also puts some responsibility onto you; if you're going to change trajectory whilst walking, for the love of god check over your shoulder to make sure someone isn't about to overtake you before you suddenly turn 90 degrees without warning, and don't just stop dead in the middle of the pavement when someone is walking behind you