[SC悬赏令] everyone laughed at me accidentally walking into the girls' bathroom. Y walk--ev

if the focus of the construction is the ACTION, then you must use the POSSESSIVE form for the noun/pronoun preceding the "-ing" participle. since that's fatally awkward to say in words, i'll provide an example:

everyone laughed at me accidentally walking into the girls' bathroom --> WRONG. sorry. this sentence would actually mean that everyone laughed at me as they were walking into the girls' bathroom.

everyone laughed at my accidentally walking into the girls' bathroom --> CORRECT, because it's the action (my walking into the bathroom, not really me) that they're laughing at.