> "One exception to this that I've found is when someone already has plans for getting rid of someone and just needs the "ammo". At that point, they will quickly become your "friend" in order to get all of the dirt on that person, and then once the deed is done, it'll be like you never existed to them."

This one hits hard. I was just a developer at the time, but I had a co-founder get really chummy with me, and I eventually discovered it was for exactly this reason: to get "ammo" against the CTO to force him out. I got fired shortly after the whole situation played out.