Wearing outside clothes on the bed is gross, and I don't understand how people do it...

I visited a friend's place recently and they just flopped onto their bed wearing the same jeans they had been wearing on the bus and sitting in a public cafe all day. I was honestly horrified.

To me, the bed is a sacred, clean space. "Outside clothes" have touched public benches, subway seats, and who knows what else. As soon as I get home, I have to change into "inside clothes" or pajamas before I even think about sitting on my sheets.

My friend thinks I’m a total germaphobe, but I think they’re sleeping in a pile of city grime. Am I overreacting, or is the no outside clothes on the bed rule a standard thing for most people? Where do you draw the line?