This didn't directly happen to me, but I witnessed it.
Me and a friend were riding in west mongolia, when we inevitably came across a smallish river crossing.
It was my turn to see if how deep the water was, so in I plunge with boots off and trousers rolled up, out in the middle of no-where. Some white guy having a splash on his foreign bike.
All of a sudden I'm lolling around in the water when this old skool 2-stroke russian motorbike and sidecar rolls up to the water's edge, with steve mcqueen mongolian riding it with his wife and kid in the sidecar.
He shoots me this look that said "hey sunshine, this is mongolia, we don't worry about water depth" which made me feel a right pillock, and he ploughs right on in.
As he got half way in he flooded the bike and all family members had to bail as it sank.