Homemade fermented coconut milk
I'd go with "certainly not safe" - and probably rotten.

Even for fermenting foods like yogurt or sauerkraut you need to follow a certain protocol to ensure the end product is safe. Yes, a pot of milk that was left out can turn into a delicious soured milk if the right bacteria grows in it. It can also turn into a nasty rotten mess.

If you want to ensure a specific product, you should add the appropriate bacteria, the traditional way would be a spoonful of an established product. Alternatively the bacteria can be obtained in liquid or dry form. This would give you a safe product. 

While it is possible to ferment coconut milk with "yogurt bacteria", it's pretty unlikely that the "desired" bacteria mysteriously appeared in your milk. So no, your coconut milk is not safe. And if you write "slimy", I assume it's simply rotten.