I don't even.
It's a meme from 4chan. It goes something like this: Japanese have a thing for incredibly shy girls. Or possibly they have different taboos over intimacy than the typical western nation. In either case, this shows in their comics and cartoons as well so several mangas have scenes where someone (usually girl) blushes madly at the mere thought of kissing or holding hands and sometimes they may even exclaim that doing something like that would be so "lewd."
4chan started joking about it and occasionally when someone (for example) posts a picture of a woman and asks "what would anon do to her?" the replies are "I would hold hands with her" and everyone then comments that "that is too lewd" or "this is a Christian board, we don't tolerate stuff like that."
That particular scene (don't know the show) had the two characters REALLY nervous about holding hands, so naturally someone took it one step further and added the pixelation to imply that hand holding is somehow comparable to sex in lewdness.
Other examples:
Note: This one actually IS hentai.
