The Hide and Sneak. Realising in time that you simply cannot say hello to this person, because you forgot if they were in your high school class, or if they’re a colleague from another department or just someone you talked to once at a flea market.
Hiding is nice, because the person will never know you saw them, if you’re talented enough. And thereby will not be offended or hurt that you didn’t say hi. However, other people will most likely wonder what you’re doing behind the butternut squashes.