Unless... you got so wet that the rain soaked through to your underwear and now your wet shorts are soaking through your new, dry costume. Yuck.
Lesson? Keep a spare pair of clean, dry underwear in your locker.
I spent a day at Busch Gardens Williamsburg two Octobers ago where it was raining so hard they opened an hour late, there was 6 inches of water around the fountain at the entrance, and they closed at 5pm because the only got 1000 people through the doors.
But it was still a great day, the park employees were happy to see anybody, and when it stopped raining for a little bit there were no lines on any of the roller coasters.
Rain is great to fall asleep to, but I don't like wandering around in the rain, to be honest. That won't stop me from enjoying a theme park. I generally keep stuff like ponchos and umbrellas on hand for that sort of weather.
On and off rain at an amusement/theme park can be just fine. We got soaked to the bone at SFGA last October - but the rides stayed open most of the time and the crowds were really light.
Several years ago I went to Kings Dominion where it rained non-stop throughout the entire day! They never closed any of the rides and I was one of 100 people in the park. I walked on everything and had a blast! However, rain hurts when you're going 70 mph on Volcano: The Blast Coaster.
All day torrential = bad. Off and on showers or a brief Orlando thunderstorm? Bring it on!
Step 2 - Type "Magic Kingdom parade during hurricane 1" into search box.
Step 3 - Sit back and be amazed.
Here's the direct link.
I remember being on parade duty several times when control screwed up and sent the parade off, only to have the storm hit after it hit the route. (It's amazing how fast the floats can go then!) Much drinking happened after those shifts.