The bit about young kids doesn't count because they're kids and can't think straight. They can't think like me. I'll take on the old people point by point.
1. How is it disgusting. Somebody has a bottle held to their lips. Disgusting things is stuff like a corpse infested with maggots, or a tarantula. Nothing like having a plastic bottle in your face.
2. It's only unhygienic is the person doing it has bleeding lips and it's gushing into the bottle. Muddy lips don't count because you can just clean it off in two seconds. They're not going to be so muddy that the mud falls in, are they?
3. Spreading germs, eh? Let's say that no-one in my household has felt ill drinking from those Sunny Delight tubs. The only way you could get ill from that is if they have some bizarre disease that gets transferred by this way. And if they did, you'd know about it.
So, I'm not saying that we should all ditch our cups and glasses and go drinking in this way. How do you expect to evenly divide drinks? I just want old farts and dopey kids to stop being so heavy on this matter. There, it's sorted.