A writing instrument has a front body with an ergonomic grasping segment asymmetrical relative to a first longitudinal plane, and a rear body asymmetrical relative to a second longitudinal plane. The rear body is capable of rotating relative to the front body about a longitudinal axis corresponding to a line of intersection between the first longitudinal plane and the second longitudinal plane, between a position adapted to gripping with a right hand and a position adapted to gripping with a left hand. The present invention also relates to a method of using this writing instrument.