Just click on the next point but don't drag the pen. This should give a sharp angle.
I know that but i am trying to draw a strait line then add points to drag. Its not a mandatory thing but i was experimenting with the pen tool today for practice and found that i could not drag an added point without a curve.
Make it a habit to keep one finger on ctrl and one on alt while working with the pen tool.
Ctrl temporarily switches to the direct selection/path selection tool (whichever is the active one). Alt switches to the convert point tool.
This lets you move and modify any point and any handle as you go along.