"Filibuster" is written nowhere in the US Constitution.
Well yeah. Not sure why you felt the need to point that out. This complaint is about parliamentary procedures, hypocrisy and divisive politics.
It's relevant in that you were talking about Republicans threatening to use it but not using it (making it seem as if Democrats haven't done the same before actually using it), and my point is: it's no where in the Constitution which Republicans always state they believe in the Constitution, and use it as a tool to win arguments (which they rarely do) in concern to it, and therefore as some Republicans have done recently in argument toward any opposition using the filibuster as a "Constitutional right" (knowing or not knowing it's not in the Constitution) to "win" in such idiotic debate and position.
Don't know if you're a Republican, or not, but it's a tool I'm sure many Republicans have used; doesn't matter if it's true, to them.