The first thing I would show them is:
82,750 Uploads; 25,715 Distributions; 112,511 Modules; 10,034 Uploaders.

And all of these packages self-test themselves on your system and in some cases customize themselves to your system.   They represent a vast library of code that is known to work.   Everything from one-line web servers to literally rocket science.

And, quite honestly, I just might stop there.   Show a cross-section of what can be done by stringing packages together.   You don’t have to wander too far into what programmers probably already know.   You don’t need to “compare” Perl, much less defend it.   By now, the language speaks for itself.   The core features of the language will be familiar to most, and I almost feel that “the language” is beside the point.

It’s useful to mention TMTOWTDI™, and also to just show a few examples of why Perl has repeatedly been called the Swiss Army® Knife of computing.   This is, very pragmatically speaking, an extremely useful language ... and in a very “boots on the ground” sort of way.   Like every language it has its quirks; so what.   Let’s talk freight, as in moving it for a living.   This thing very efficiently does what you most need to get done.   Just keep showing synopsis after synopsis of that.

I still remember this quote:   Actum Ne Agas = Do Not Do A Thing Already Done.   And I think that this notion really summarizes Perl.   Any new code that you write, in order to solve a problem, pales against what you don’t have to write.   To any professional miracle-worker, that’s “Priceless.™”

This is a language that seasoned practitioners, who of course know a great many languages and more-or-less switch between them throughout the day, tend to keep coming back to.   There is a reason.

Last but not least, send them here.   Tell them about PerlMonks and specifically encourage them to browse here.   It is one of the best sites on the web in many ways, and not just with regards to Perl.