I'll say 'hi' to someone if I see them, but I'll also go out of my way to avoid running into people I work with on the street. For example, if I see someone walking ahead of me, I'll actually walk a block out of my way to avoid a forced, awkward conversation. I walk at a really fast pace so I usually catch up to people pretty quickly. It's always awkward when I'm walking and catch up on someone only to say 'Hi. Well, see ya.', so I avoid that. Also, every once & a while I'll run into someone on my way to the train & it just so happens they're on their way to the train too so they start up a conversation. Then I have to walk infuriatingly slow to carry on the conversation. Then if they're taking the c-train the same direction I am it's even worse. I really enjoy just listening to music and tuning everything & everyone out on my commute home. It helps me relax after a long day and the absolute worst thing is when I get stuck having a 30 minute conversation about the weather with someone on the train.
Same thing with taking the elevator down to grab lunch. If there is someone waiting for the elevator that I'd really rather not talk to, I'll walk by them with a smile & pretend to go to the washroom so I don't get stuck walking the +15s with them.
I probably sound really anti-social.