I understand that you are upset that you received a low ball offer on your house... but now is not the time to get emotional about it.
The last thing you want to do is get ticked off and refuse to respond to the low ball offer.
The good news is that the hardest part is done... you found someone who is interested in your home.
What you need to do now is clean up the terms of their offer, and isolate the price issue.
For example, if they have a 21 day loan contingency, counter them at 18 days. If they have a 17 day inspection contingency, counter them at 10 days.
Clean up all those bad terms and isolate just the price. Counter them at full asking price if you want.
By doing this, when they counter you back, they have accepted your revised terms of the offer, and you are now only focusing on price... nothing else.
At this point, your agent has to do a good job of negotiating and bringing the buyer up.
You would be amazed at how many buyers I have dealt with that are just bluffing. They love the house and eventually come up in their purchase price.
Stick with them, because after all, they have shown an interest in your home.