People didn't look up. The things they needed were usually at eye level, or lower. And three young boys plotting their battle strategy in a Silly String War certainly didn't think it was necessary to look at the ceiling.
Which is why they didn't see Peter carefully crawling along it. His shoes he'd left down in his apartment, since his rendition of this ability didn't come with a shiny red and blue suit.
When he was directly over head, Peter turned over, holding himself to the ceiling by his feet, and stretched out both hands. In each was a bottle.
"Death from above!" he called out, and started to spray the boys mercilessly.