Yes agreed these don't just push in, well they do but they need to have the core pulled to tighten them up.

i installed them about 3 weeks ago....i am talking from experience.
you simply just push the top in..... and the bottom part that comes out of the thick side expands

no they dont you push the base in flush and you then push the skinny part it, they dont back out

You guys are talking about two different things. There are two types used to affix the arches:

https://dl.dropboxusercontent.com/u/...BMW-Rivets.jpg

The one on the top you push in and then use a rivet gun to pull the center pin to expand the bottom and at that point the pin breaks off flush with the surface. This type cannot be removed without destroying it.

The one on the bottom, you push it in and then push the center pin in to expand it. A pry tool can then be used to pull the center pin back out and remove it.

You need a plastic rivet gun for these. Something like the Marsen klik lok