My rear view mirror came off and I don't know to to put it back on. It came of the ball joint. I tried to push it back if but it has a plastic thing on the mirror's hole, where the ball should go. Would it be easier if I took of the mount and forced it in than put it back on? Please help!

 

I have never taken one of those mirrors apart, but here's what I would do.
First, carefully remove the mount arm from the window ( remove cover at mount base and loosen set screw so the mount slides off the lug)

Secondly, see if the plastic part in the hole on the back of the mirror will rotate to show a hole, it is most likely a plastic bushing designed to allow grip and smooth movement of the ball joint.(also check to see if there are any other signs of fasteners/screws that affect the socket joint)

Thirdly, apply a very small amount of lubricant to the ball of the mount, and attempt to reinsert the ball into the socket with firm force, if it does not go in with a reasonable amount of effort, make sure things are aligned and try once more.

If it does reinsert with no problems, check for smooth operation of the joint and ensure that it doesn't wobble excessively in the socket, then reattach to the window lug, not over-tightening it... if it wobbles after assembly, just replace it. If you aren't able to reinsert it, I would simply go to a scrapyard and retrieve another.

Again, not having seen one of these mirrors fully disassembled, I can only give you what I imagine to be the way the part is assembled, as the FSM only shows disassembly/assembly at the window lug.

Good luck