A significant problem is earbuds. People wear them anywhere: walking in the middle of auto traffic, in saunas and pools. Unless a cellphone is visible one may not realize a person is in a conversation.

Years ago It was depressing to see someone talking to himself in the middle of a parking lot; now it's an everyday occurrence but not madness b/c there's a real conversation.

Every now and then I ponder whether the cellphone and earbuds combo hasn't become the perfect disguise for schizophrenics.