If you send someone out to do a job, you do not want him being lazy and laying around (sluggard). If you have someone this lazy working for you, it is painful to you just like it is painful to put pure vinegar on your teeth. It makes them burn.
Defined: As the acidity of vinegar causes the unpleasantness and pain to the teeth, and by softening and dissolving alkali of the bone, impairs their texture, and renders them incapable of grinding; Smoke in your eyes causes you to cry, and I believe that is what is meant here. Truly someone who is supposed to do a job and won’t, will bring you tears.
You can imagine how God feels when He calls us to do a job for him and we are too lazy to carry it out.
Defined: As smoke, by irritating the tender vessels, causes the eyes to smart, and prevents distinct vision; so a sluggish messenger is a continual vexation and loss to those by whom he is employed (see Isa 65:5).
Under Gods command 