Ok here's my made up version of a crossbow. It's kinda like a bic pen crossbow on a larger scale. I used gorilla glue on all the joints of the body, but hot glue would probably work.
Step 1: Materials
Here's what you need:
7 Popsicle sticks
Pen tube (pen minus the writing part and end cap)
Chip clip or some other strong clip (not a clothes pin)
Gorilla glue or hot glue
Bamboo skewers for ammo
Step 2: Make the body
Start by gluing a popsicle stick perpendicular to two others as shown in the first picture. Then glue another one down the middle of the two parallel sticks, like the picture. I used other popsicle sticks to support it. Then, just glue two more just like the front half of the body, but without the cross piece. Make a notch in each end of the cross piece.
Step 3: Add the pen tube and clip
Glue the pen tube in the center of the front half of the body, this will guide the arrow as it goes out. Now just clip the clip onto the end of the whole thing and put some glue on it so it only opens to the top. Add the rubber band as shown wrapping it around the notches and onto the end of the pen. It is helpful to put a notch in the end of the pen so the rubber band doesn't slip off and to help load it.
Step 4: Load and fire
Shove a bamboo skewer in the pen tube and center it on the rubber band so it stays. Push it all the way in, center it on the body, and clip it. It improves the flight and makes it easier to load if you add a little bit of electrical tape on the front of a skewer. Fire by just unclipping the arrow.