The ornamental design for a ballpointpen, as shown and described.
1. Ballpoint pen
1.1 : Perspective
1.2 : Front
1.3 : Top
1.4 : Bottom
1.5 : Left
1.6 : Right
1.7 : Enlarged top view
1.8 : Enlarged bottom view
Back views are omitted because they are mirror images of the front views; parts shown by broken lines do not constitute claimed designs; thin lines represent surface shading to show the contours of the article only, and do not represent ornamentation or decoration.