Of all the egregious things this man has done as president this is probably the most minor (and really isn't wrong).
The President is not a member of the military and as such returning a salute is arguably a breech of protocol. So whether it's a proper salute or a flippant one with a coffee in his hand is a non issue. The tradition of returning the Marines' salutes while getting off Marine 1 is a Reagan era invention (not long standing tradition).
But hell, if this is what we can impeach him on, why not.
Yeah I see what your saying but just a little common courtesy goes a long way.
Don't pick a fight with an old man. If he is too old to Fight, he'll just kill you.