It is used to describe a person who has just had short, casual,vigorous sexual activities or someone who may be about to.
Friend 1 says 'did u have sex with that guy last night?'
friend 2 replies 'yeah, I got Baxter'd'' or 'he 'baxter'd' me'
Another example would be seeing two people leave and exclaiming to friends...
'She is gonna get 'baxter'd'
You could also ask a friend if anyone got 'baxter'd last night?'