calling bitcoin a ponzi scheme
but I still call it a huge bubble
If you couldn't figure out something as simple as why a Ponzi scheme is how do you expect to figure out what a bubble is. The concept of a bubble is much simple than the concept of a Ponzi scheme!
but at over 64K a piece
What you need to understand is that just because a number is big that doesn't mean that number represents a "bubble"! If you are scared when seeing $64k what are you going to do when you see $500k this year?