If you're going to walk through a crowded place holding hands and neither of you is handicapped, then you're just being inconsiderate to anyone who's trying to get past. And if you're going to walk really slow, at least leave room for people to overtake you.
Anyone who walks abreast on the pavement forcing people coming the other way to step into the road because they can't be bothered to move aside is just plain rude. When some people did it to me tonight I wanted to barge through them shouting, "CAN'T YOU SEE ME HERE?"