Clothes should be washed after wearing them once. You don't have to fall in the mud or spill something on your shirt before it needs to be washed. Germs are everywhere and it takes no time at all for your clothes to be filled with them. Just walking into a smoke filled room means your clothes could u se a good wash. If this is not done, why bother to bathe? You are putting all of the old dirt onto your clean body.
No, something isn't dirty after wearing it once, because most clothes don't get soiled that fast. T-shirts and undergarments smell after wearing them for a day, but clothes like coats and pants can be worn a few times before they are dirty. It depends on the type of clothing, but definitely not for most types of clothes, after one use.