Just to make sure you know: a pen filled with a blasting cap alone (no RDX) is more than capable of reducing a hand to a pink mist. These aren't toys, and are not at all sutible for pranks.

If pen functionality doesn't matter, then the clicker button should be replaced with a push button switch. That would go into a 555 timer circuit, which would then fire a small relay which would in turn activate a 3v battery + nichrome wire circuit. The time delay is determined by what resistors and capacitors you use with the 555 timer.

The nichrome would be inside of a blasting cap (probably .2g or so or acetone peroxide, maybe lead azide if you have NaN3). The cap would be placed directly on top of as much RDX as would fit in the pen tube. All of the pen parts should be removed to more effectively utilize space (assuming the pen doesn't need to work as a pen).

Just making sure you know the risks.

I don't want to find a news report saying "heisenberg teaches now inmate Agent Madhatter how to blow off cop's hands with mock pens, nationwide manhunt ensues."

I don't get the joke?

yea  it all fake ! no such thing in the world as a binary exsplosive

I can't resist.

ANAl.

Ammonium nitrate/aluminum. Also, there's ANNM, ANFO, ANNG, etc. There are lots of binary explosives, just none nearly as powerful as the one in the vid.

it's the butt of the joke lamo !

getting off topic