Is a Kohen (shomer torah/mitzvot ben torah- though not a talmid hacham) permitted to be mezalzez himself if asked to do something by his office manager at work, for example- take a large very noticeable amount of big trash bag(s) out in front of his office? is it a problem even if the kohen is mochel his kavod to the person who asked him to do it?
The primary obligation of giving a Kohen the honor he is due applies to the Yisrael, and not to the Kohen himself.
Therefore, poskim address the question of a Kohen foregoing his honor not in terms of the Kohen himself, but rather in terms of the Yisrael: Does it help for a Kohen to forgo his honor, or not?
Even for the question here, the main question is not whether the Kohen can take out the garbage — if told to do so by his boss, and obligated to do so by his work contract, he can do the job, and is not obligated to quit because of this. Rather, the question is whether or not the boss is permitted to ask him to do it, based on the assumption that he forgoes his honor.
In answer to this question, the Rema (128:45) rules that a Kohen can forgo his honor, and the prohibition to “use” him applies only where he did not forgo his honor.
This ruling is based on the Mordechai (Gittin 451), citing from Rabbeinu Peter. It is noteworthy that the Rambam disputes this, and writes that a Kohen cannot forego his honor.
The Taz adds that the Kohen is able to forego his honor where it is for his own benefit. In the case of a work agreement, the arrangement is to some degree for the benefit of the Kohen, and it appears that one can rely on this to be lenient. Having said this, if taking out the garbage isn’t “part of the job,” it is certainly right to find somebody else to do it, even if the Kohen forgoes his honor.