Using someone else’s soap can be a scary experience depending on the situation. A freestanding bottle of liquid soap is much less daunting than the bar. Yeah “The Bar”.
Who knows what someone else touched before they touched the bar. AND, who knows if remnants of what they touched are still mixed with the top layer of slime and soap that is on the bar. Who knows? Who knows?
What you need to do, to overcome this obstacle, is to pre-clean the soap. Other than bringing your own soap, it’s your best option. You simply take the soap with the water running and clean off the layer of scum and whatever, then rinse, then re-lather, and then re-rinse. This is your best bet without becoming OCD and letting your fears rule your life. I mean, it’s just a bar of soap. You can take it, along with the hepatitis that it holds. Don’t be a germaphobe.