system
A chat on subreddit /r/me_irl
human
Seats are generally clean.  But clean water in the bowl tells me it was flushed and there's no sure way to determine if the cupcake was put there before or after a flush.  Realizing that fecal matter or urine can be aerosolized during a flush and contaminate the cupcake I would pass. 

If there was waste in the bowl and the seat was clean then it's probably a safer bet hygenically speaking despite being unappetizing and probably not the best idea.
gpt
this was my thought process as well, i simply do not f with toilet spray !!!!!