Yet Here's a Spot

Spot (O.E.D.): 1.a. a small part of the surface of a thing distinguished by colour, texture,                       
                               etc... 
                           c. a pimple
                           e. a moral blemish or stain 

Of course, I sympathise with Lady Macbeth. One cannot but agree with her heartfelt wish, 'Out damned spot. Out, I say'. These things always do crop up on the eve of a big occasion. 
Such a little word, yet so versatile- spot illustration, penalty spot, in a tight spot, spot welding, spot check. And spots are always described as 'angry'. You don't get mild-mannered pimples or cheery zits. 

Above, a spot illustration, of course.