[header] How to make an airsoft grenade [title] Open a regular plastic easter egg. [title] Drill or cut out the little hole in the bottom. [title] Insert a firecracker (types may vary), and stick the wick out of the hole (m90's are cheap, small, and very powerful). 
[step] Be sure to make the wick long enough for someone to be able to get away in time. [title] Fill the grenade with some inexpensive or cheap 6 mm plastic bbs.