A woman was told to use the men's toilets at Worthing station because staff refused to open the recently-cleaned women's facilities.
But the men's were so filthy she hopped on a bus to a supermarket to use its loos instead.
Lynn Knee, of Links Road in Lancing, has complained to her MP about the late-night incident.
Mrs Knee, 51, was waiting with her husband for a train that was delayed by more than an hour.
She said: "It had happened before that the toilets were closed but I had just asked one of the staff if they could open them for me to nip in.
"But this time they said they wouldn't because they had just been cleaned."
When Mrs Knee saw the state of the men's toilets she refused to go in.
She said: "Why can't they keep the toilets open until the last train has gone?"
A spokesman for rail operator South Central said: "We try to keep the station toilets open all the time but sometimes, because of vandalism or lack of staff, it is not possible."
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