Sorry if someone has already has this grenade idea or name, but it just was so simple.
The grenade does have a pin, but it is optional.
The grenade will look like this when it is finished:
Step 1: Parts List
Red Connectors - 16 or 20
Orange Connectors - 8 or 10
Yellow Connectors - 0 or 2
Gather up all the parts and then continue.
Step 2: The Shell
Just follow the pictures.
Step 3: The Rubberbands
Step 4: The Filling
Step 5: The Pin (Optional)
... well, you know what I was about to say.