I meet my T in the street from time to time. His office is not far from where I work, and I pass by on my way to and from work in the morning and evening. I rather like seeing him; he always smiles warmly and says hello, and I smile back and say hello, just like with any other acquaintance. I suspect that he wouldn't say hello first if either one of us was walking together with someone else, though. And I would never do more than just say hi - there is no way I would stop and chat. But as I say, I like the minimally interactional meetings.