The rain falls over an extended period of time, not all at once as one glob. Only several drops are hitting you at any given instant in the rain, so you are only subjected to minuscule amounts of force at any given instant.

The difference would be like standing in the shower for 40 minutes, versus being hit my an entire tub full of water going at the same speed all at once.

I remember during the Khan Academy controversy a few years back, an educator commented on reddit about the difficulty in teaching some kids about rates. Some kids just don't get rates. They think of speed as something like "a feeling of intensity." They just don't have an abstract, generalized understanding of "N things per unit time."

Think about that for a moment. Think about all of the potential for miscommunication.