When it comes to piss, as of now, you only have three options: Wolves, Arion, Arion and Hayden.
1) Wolves: Player losing fight, with the wolf having low libido. You can find the wolves in the forest area.
2) Arion: two options: a) Player losing to Arion, Arion will piss on the player.
b)Player winning fight against Arion, gives the player the option to piss on Arion.
3) Part of Arion's bath quest while taking his side. During the quest you confront Hayden (Arion's stalker) and you get the option to get piss involved.
You can find Arion in Bareshade at the stables, but you have to meet him first on the track and then invite him to Bareshade and have a mini event at the tavern.
I don't know anything about new piss options, but I do think that Hyao or the other writers might add some more piss options in game.