When a animation like "Acts_AidlPercMstpSlowWrflDnon_pissing" is performed on a player unit the unit just stays still with holstered weapon if a weapon is present. It won't work with any kind of command. I tried [playMove, switchMove,playAction,playActionNow,playGesture].
A AI unit is performing the animation as displayed in the animation selection gui.
Addition:
It's not only in SP. In MP you can see others doing the anim but for yourself you just stand there like a fool.