Male and female Equus grevyi. I believe the male will typically quite often harrass the females, but, in this case, it was the other way around -- this female here spent 10 minutes or so chasing the male around, kicking the air near him, seemingly 'playfully' biting/nibbling, and even mounting him a couple of times.
The male seemed completely disinterested throughout all of this attention, and was eager to get back to grazing again once it had all calmed down.