Quickly show the Tabs dialog box by double-clicking on the ruler just below the markings and the gray line.  Make sure you double-click at the bottom of the ruler, not at the top. 

Tabs dialog box

NOTE:  If you double-click at the top of the ruler, then the Page Setup dialog box appears.

If you set a tab stop when you double-click on the ruler, then you can delete the new tab in the Tabs dialog box or you can drag the Tab off the ruler.