When R' Shmelke of Nikolsburg came to Nikolburg, he was receiving compliments from people. He suddenly stopped and said, "Before we continue, I need some time." He went into another room, and those waiting outside could hear him praising himself: "You're so wise, R' Shmelke! You're a great tzaddik! You're a gadol hador!"
When he came back, they were puzzled. "Rebbe, what was that about?" R' Shmelke explained: "When someone gives himself kavod, it means nothing. Real kavod is when other people give you honor. I wanted to practice so that the kavod others were giving me would have no greater effect on me than the kavod I give myself, which is worth nothing."
This, he said, is the meaning of the Mishnah,10 יְהִי כְבֹוד חֲבֵרְךָ חָבִיב עָלֶיךָ כְּשֶׁלָּךְ, let your friend's honor be as dear to you as your own. He explained it differently: the kavod your friend gives you should be as dear to you as the honor you give yourself, meaning it's all meaningless.
10 Avos 2:15.