I still haven't found a slime. I am sad about that.
I have only ever seen one, it was at the bottom of my mine at 2-3 above Bedrock level. As far as I know, they can't hurt you, they just hop around and leave slime balls.
lol, @ShadowRex129 don't get me started on dumb wolfs, iv had them die by cacti, lava, i had one who glitched and would not swim up so he drowned in my lake(thing), there's also the one who teleported into a wall, one who jumped off a cliff after a skeleton who shot me, etc etc. so again, don't get me started on dumb wolfs.