After minor collision,(another vehicle struck rear of mine and slid underneath) noticed my muffler is jammed forward and up so now touching undercarriage of car. Is this a problem?
Yes. Body damage too? His insurance should cover all repairs.
If exhaust was the only damage and you let the other guy off the hook. Just take it to an independent muffler shop. I suspect a fairly inexpensive repair.
Yes, dangerous if it leaks and highly annoying if it is hitting anything while you drive.
It’s very hot and it’s now transferring that heat to whatever it’s touching. I’d call that a problem.
Even if the OP doesn’t smell any exhaust fumes, there is a possibility that CO is now leaking into the vehicle’s interior.
I suggest that the OP drive with at least one window open, and drive directly to a muffler shop tomorrow.