What constitutes as an "enemy"? Can for some reason a PC declare another PC an enemy at any point?
For example, we will take this first level Warden spell which puts spikes around an enemy that will only effect enemies:
The earth rises in concert with your attack, driving sharp spikes of wood and stone up toward your foe even as your weapon slams down.
Standard Action Melee weapon
Target: One creature
Attack: Strength vs. AC
Hit:1[W] + Strength Modifier damage. Until the end of your next turn, the target's space and each square adjacent to it are filled with spikes. Any enemy that enters this spike-filled area or starts its turn there takes 5 damage.
I believe this spells is worded this way because it assumes you will have melee pcs in the group, which if it didn't say enemy, they would be effected by the spikes being adjacent to the enemy. What if mid fight the warden declares one of the other pcs an enemy. Would the spikes then work against the pc?
If so, would the effect take place immediately?
Edit: My case - I run a game that has a Warden, Shaman, and a Fighter. The Warden and the fighter don't get a long to well because of backgrounds (warden is a shifter and the fighter calls her a dog all the time...it makes for good rp most times). With yelling being a free action during battle, she playfully said he was an enemy. I didn't take it serious in this situation but they have thrown hands at each other in game on multiple occasions so I could see her calling him an enemy at any point if he presses the wrong button.