Word for introducing people without knowing their names

Solution 1:

Perhaps you're referring to the idiom mind went blank.

Edit: I'm assuming you're referring to the sudden inability to recall information that you already know, in general. This could be someone's name (as in the example you provided), or it could be, say, the sudden inability to remember some factoid during an exam.

If I'm wrong about that assumption, however, there's this word:

lethonomia: 1. A tendency to forget names. 2. The inability to recall the right name.

Solution 2:

It seems that people involved in the study of memory, lexical retrieval, and cognitive psychology call these tip-of-the-tongue experiences. This is an interesting article from New Scientist. Here's a brief excerpt:

More likely, tip-of-the-tongue experiences occur when we're trying to recall rarely used words, Pyers says. (Note: The article says Pyers is a psychologist at Wellesley College in Massachusetts.)

"People often have tip of the tongue experiences for proper names, again because we don't use them very frequently," she adds. *

(*Inconsistent hyphenation of tip-of-the-tongue experiences in original.)

Solution 3:

Not remembering names is called a tartle. It's a word from Scotland.