I think elbows on the table are fine sanitary wise - I'm pretty sure historically the reason people didn't do it was to keep their body safe from the unsanitary table. So it's sort of a "don't eat food that's fallen on the floor" issue which no longer is of concern.
But I do think feet on the booth is a sanitary issue - and as others mentioned it's even more serious if it's bare feet up there. Fungus and other nasty things can be in feet
So it's a double problem. If you put your feet up there not only are you exposing others to your foot fungal germs - but you could easily pick up something really nasty from other people who had done that before you. Fungal issues can take a long time to heal up from.
So I don't think of it as etiquette like "don't clap to your own toast". I think of it as etiquette like "cook chicken before you eat it"
