Reb Zalman Moshe and Reb Dovid Horodoker were farbrenging together. In the middle, RZM asked RDH "Dovid, tell me the truth, do you have ahava veyirah? First he tried to get out of it, but RZM would not relent, and finally picked up a bottle and warned ", "if you don't give me a straight answer, you're getting this bottle on your head!" So, left with no choice, RDH replied "ahava veyirah, nu, a mohl kitzelt zich".

The story is relatively known, but when Rabbi Aronow told the story, he described RZM and RDH as being אויף דו. No one knew what "אויף דו" means (nor did anyone since who I ever told it over to). So he explained: When you speak To an older person, deserving of respect, you have to address them as איהר. But 2 people who are equals, can address each other as "du". When we want to describe that these two chassidim were of similar age and stature, we describe them as being אויף דו. היה מרגלא בפומיה שהוא יהי' חסיד עד זיבולא בתרייתא