It's a fair and valid point to raise that coughing at concerts between
movements and otherwise is gratuitous.  Unfortunately, the "letting it out"
has become social convention, even among lovers of music (as opposed to
poseurs).  And even for those determined not to cough, there's something
of that contagious yawn effect about it.  (I just yawned involuntarily as
I typed that.)

But, more importantly, NEVER EVER stifle a sneeze.  As much as a sneeze may
ruin things for a few concertgoers, there's a big risk.  A friend of mine
is almost completely deaf thanks to stifling a sneeze.  And it wasn't just
a fluke for him.  Apparently, stifling a sneeze creates even more cranial
pressure than sneezing, and it is well-documented by doctors to be a
dangerous thing to do.

Ben Malkevitch