This is also my FIRST instructable so be nice ;-)
(Sorry for the blurry pictures, my mobile camera kinda sucks)
Step 1: What You Need
To the launch you will need: a bottle (kinda important) and a pump (Realy important). And if you want: something to keep it steady when launch
Step 2: Drill It!
Now you are gunna drill a hole in the bottle top that maches the pen size.
Step 3: Glue It!
Step 4: And Cut!
Now it's time to cut the pen.