For those of us who aren't great with people, we figure that silence is always the safest bet. If you're an introvert, you spend so much of your time wishing that other people would just shut the hell up that you figure you're doing everyone a favor. So, you run into a co-worker at the mall and think it's better to pass by in silence than do an awkward stop-and-chat that you'd probably screw up anyway.
Then, after you pass by this person, you hear them in the aisle behind you mutter, "a*****e."
"Maybe next time I'll just forget to pick up my roller skates from the stairs."
So What's the Problem?
This is literally the most frequent social mistake I see in my day to day. You didn't respond to the party invitation. You didn't reply to their funny text with a smiley. You didn't wish them a happy birthday. Now they're bitter and you're confused because, well, who would ever assume that silence is an insult?
Lots of people. In fact, to certain personality types, not speaking is the most bitter insult possible. Yes, worse than "shitblimp."