"What was I doing? Why was I always alone and secretive? Was it legal? Was it dangerous?" (20.37)
Here we have Griffin talking about his landlord in London. Or rather, it's more like Griffin speaking <em>for</em> the landlord, who is worried that Griffin is up to no good. And the landlord's evidence that Griffin is bad news? He's always alone.
"By this time I knew he was alone in the house, and so I made no more ado, but knocked him on the head." (23.20)
Sometimes being alone is associated with being vulnerable. Here Griffin tells Kemp how he took out the costume-shop owner: as soon as Griffin realizes the guy is alone, bam, he knocks him out. (You'd almost imagine that Griffin would empathize with people who are alone like him, but no – he doesn't seem to care about anyone.)
"I went into a place and was already ordering lunch, when it occurred to me that I could not eat unless I exposed my invisible face." (23.44)
We like this quote because it takes something very social – eating together – and shows how Griffin is on the outside. He can never eat around people again. We could make a joke here about pizza parties, but it's kind of serious: eating together is one way people show that they belong together.