you could try asking them

I have. You point out the verses to them and they say things like "Well all I know is that God is just." Or they just say "Hmm." What I want to know is what a thinking sort of hell-denying Christian says.

Or reading their books

Since this is essentially a heretical position, I'm not sure how heavily it's defended in the literature. Still, I do have in my bookshelf an anthology containing a universalist essay by Marilyn McCord Adams, where she states that "I do not regard Scripture as infallible [... but ...] I do not regard my universalist theology as un-Scriptural, because I believe the theme of definitive divine triumph is central to the Bible". She seems to want to reject the Bible and accept it too.

You could even think up good arguments yourself for reconciling the belief with the verses.

I think the most coherent Christian position would be: There is a God. Various interesting things happened at God's doing, including Jesus and his miracles. The people who witnessed all these events wrote about them, but invariably these accounts are half fiction or worse. Paul is clearly a charlatan.

But nobody seems to believe this: Christians who think the Bible is fallible nevertheless act as if it is mostly right.

flaunting Biblical quotations [...] does not make a good argument

It's necessary when dealing with the doublethink of people who want to take the Bible as divine yet reject key parts of it.

going "nyah! nyah!"

Note that this sort of comment provokes an automatic reaction to fight back, rather than to consider whether you might be correct.