Perceived increase in confidence, machismo, bravado, strength, cage-fighting abilites (etc.) from a public chat room or IM user based PURELY upon the anonymity of the "tough talker" to the person they are "tough talking to".
A 6-foot, 130lb. dork threatening to "kick your ass" when you disagree with his opinion on the relevance of Linux, Firefox, Open Source, Dungeons and Dragons or whatever other lame activity the "net muscled" geek in interested in.
"The dork is using his Net Muscles to bully the chat room into agreeing with him."