$_="uccsm jhvkqldtr oee hofaxrtaajshkebuwelrnpitgnpry!";
$_= join$\,sort/(..)/g;
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Right now I've taken out the and print part. The way this string is set up is that he attaches a letter to each letter in the 'just another perl hacker.' He sets it up somewhat like this: "bu aj cs ...". He sorts on the first letter, which is in alphabetical order; now $_ looks something like this:

aj
bu
cs

and print ucfirst join$/,/.(.)/g;
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here he matches each of the two letter pair, but only prints the seconde letter, thus printing his japh.