Need help bricking iPhone

Hello all..I got off the phone with Apple Care today, and after 2 hours of making up false errors, they agreed to send me a replacement if mine proves faulty.

But now, I'm afraid to send them mine and then have them identify it as a modded phone. SO, the question is, how can I render my phone COMPLETELY inoperable, to the point that restoring it is nearly impossible, and would take more effort then it's worth.

Thanks in advance...

--Foy

EDIT: Sorry for repost, please post in this one so I get notified..hehe.

Plug you iphone out somewhere during "Restoring Iphone Firmware", I had to try multiple times to brick it. It makes the screen go blank. while if you still connect it to itunes, its in dfu mode and will tell you to restore the phone, so thats ur best bet. Nothing on screen=GOOD!

So, does it still give them the option to restore?

For example, if I did that, and now I wanted to restore it back (Which I wouldn't, just saying) would I be able to restore it using iTunes?

Thanks, and also, at what point do I need to unplug it?