By The Nation
The passenger, whose Facebook account is Nidtayaporn Songsri, posted a photo showing a dirty seat flanked by two other passengers.
She criticised the woman for fleeing at Phra Khanong without cleaning the seat.
After six hours, the post drew over 4,100 reactions, 5,600 shares and 31 comments.
Some comments said the woman might have had health problems.
The Skytrain has no toilets despite repeated calls from passengers.