B4ck = Back
Can I touch them? - Most likely talking about Piro's ears, possibly still referencing FLCL episode 3.
Listening to - In Johnny the Homicidal Maniac issue 3, a similar note points out what song Johnny is listening to on his headphones while on a violent rampage.
Last Regrets - opening theme of the Kanon dating sim game.
AppleCare - Piro's rant under strip [511] explains his grudge with AppleCare.

Piro speaks:
I'd like to get an ipod, but i can't justify getting one, and with the current buzz over the silly little mini ipods, i couldnt resist the dig.
btw, i'm cool with Applecare, really. They did a great job fixing seraphim's machine. I just couldnt resist the little dig, thats all :P

You just know she's gonna have problems. - A similar line occurred in Johnny the Homicidal Maniac issue 1.
Piro's final line is also reminiscent of a line from Johnny the Homicidal Maniac.