Well, I am a fencer (a sport using the western concept of swordplay as it's basis) and my weapon of choice is the foil (A sport representation of a dueling weapon. Touches (a touch equals a single point. Touché is French for "touch", and when one responds to a point in an argument with the word they are simply recognizing that a person has made a valid point) are made by applying the point of the weapon to the target area (represented by the grey area on my avatar as this is a metallic vest that acts as part of an electrical circuit used to help judge and score the sport. The weapon uses right of way rules which, if we ignore useless complexity for the sake of brevity basically means that once a person initiates a valid offensive action (that is, any action with the potential to land a touch), the other person is required to defend against it. Thus if one person attacks and the other person choose to not defend themselves but simply counter attacks and both parties land a touch, the attacker's action is the one that counts (be it a valid touch or one that is off target)). The avatar is also a fencer using a foil. That said, this fencer is using an odd mix of styles and is holding his weapon in a fashion more suitable to the Epee (the Epee allows for valid touches on any part of the opponent and thus the weapon is held level to protect the wrist and forearm. In foil, the weapon is generally held at an angle as this position allows for a more rapid transition between offense and defense) and his rear arm is held in the classical style (I keep my arm low and behind me, personally).
I chose this avatar because it was simple and striking. Plus, I rarely appear in photos and indeed there is only one known photo of me fencing.