All I was able to find was these 2 blog posts which basically say the same thing. Let me just quote it from one of those blogs
The “Taxi-Cab Fallacy” is committed when one hops in and assumes a certain system of thought or worldview in an attempt to make a particular point but then jumps out of the system of thought when it suits their fancy.I'm not sure I really understand this, and I did a quick scan of the comments of both blogs and was unable to find a good example. It seems that the complaint is that atheists are picking certain details out of the bible and then asking the theist to answer without being allowed to use other things from the bible. Depending on how it goes, I could see this being valid or not. It's hard to judge without an example. Although I will say, my initial reaction is that this sounds like a proof by contradiction. This is where you start with certain assumptions and show that they lead to nonsense, thereby proving that those assumptions were incorrect.
Ok, now I am going to go look at the iron chariots page. They have the example of challenging a theist as to whether it was morally correct for Abraham to go up to the mountain to sacrifice his son. If the theist says yes, the the Atheist can ask if it was moral because God commanded it or if God commanded it because it is moral. If the theist says that God commanded it because it is moral then the atheist could ask for a non-biblical answer as to why that is moral and then is when the theist would complain of taxicab fallacy. Which certainly seems like a fraudulent claim to me. I'm guessing that the theist would try to argue taxicab fallacy without everything spelled out so nice and things get lost in the shuffle or something.
I was just not satisfied with this, so I waded back into the video from above, I found it at around 24 minutes on the video of the Q and A (actually someone asks a fairly stupid question at 22:30, Krauss rephrases it in a less stupid way at about 23:00 and then WLC responds afterward)
Basically Krauss said that people want to stop asking why at some point, so they say God. This gives them a reason to stop asking why and it is intellectual laziness. He says that there may not be an ultimate answer. Craig then says that the arbitrary point to stop is the universe and the Theists are the ones that are going further. He says that stopping at the universe is the taxicab fallacy. As far as I can tell, this doesn't mesh with the definition I found elsewhere and described above at all. Honestly, it looks to me like he throws it out there when he wants to sound smart and doesn't have a real fallacy to cite.
I'm pretty irritated here as this seems totally dishonest to me. I could be totally wrong here and if someone sees me misunderstanding something please point it out, but if this was a real fallacy WLC would properly explain it instead of just throwing it out offhand here and there.