It's not so much the straddle rides, but rides you step down into, or up out of that have flash potential. Space mountain has been brought up. I would add kali river rapids to that list of rides to be cautious on. While seated myself, a young lady stepped into the ride and paused there on the step for what seemed a long time to me. She was unaware that owing to her position and posture, me and my neighbors were eye to eye with her unobstructed nethers.
She was unencumbered, beyond the ineffectual dress skirt, by any other attempt to rein that in down there. Generally I'm far from a prude, a panty flash is not the end of the world in my household but ... I had to cough politely to get this kind soul to drop the curtain on that show, so to speak.