A nerfstick is the tool by which a moderator or admin on an online forum strikes down on bad posts and posters. It is similar to, but has more uses than the ban hammer.
This use of the term seems to have originated from a moderator on the Secret World forums.
Example 1:
Sappho: "I have a very largenerf-stick at my disposal, and I'm not afraid to use it"
Example 2:
User: Where is the nerfstick Sappho? Are you getting soft on us?
A nickname for all of the various memory sticks that plug into USB outlets on modern computers, especially those with a string or lanyard that nerds use to hang them around their necks.