" So why did he pull down his pants before he ran to the bathroom?"
The short answer is for dramatic and visual effect. When this was originally conceived it was supposed to be somewhat like an interpretive  or ballet in time with Mozart's Requiem (so there really were no rules starting out just 3 main things that had to happen). Here again its using editing and camera to tell a story more since there was no absolutely no dialogue. I had to make a literal 4-6 foot ( about 7 steps)  run to the bathroom seem like an eternity. And lets just face it watching someone run with their pants around their ankles in slow motion is plays out better  than just a tight cheeked stride (with minimal urgency).

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