I just need to ask you if I can ignore someone on the street whom I know by looking at my watch so I can pretend I don't see them?
Why do you want to ignore them instead of greeting them?
I don't want to waste my time with them.
I know it can be annoying sometimes to have to greet people you pass by, but it's rude to ignore someone you know. They will feel hurt if they think you are intentionally ignoring them.
It's not rude if it's my choice to ignore someone I just don't want to talk to them, so let me do what I want.
Think about how much of an impact a small greeting from you might have on their day. They might be having a really rough day, but that small gesture from you could really lift their spirits! Reasons like that are why you should take the small moment to say hello instead of ignoring them.