Abstract: A writing instrument having a selective engagement mechanism includes a first barrel portion with a writing tip and a second barrel portion. A docking collar with male projections extending laterally therefrom is associated with one of the first and second barrel portions, and for each male projection, at least one complementary track is provided in a track-carrying member associated with the other of the first and second barrel portions. A biasing element, such as a gasket, facilitates securement of the first and second barrel portions when engaged with one another.