Way back in the days of p-g-qvm, we used to have a feature called g_specASpec. Basically, it let you spectate spectators, but it had logic to prevent loops.
However, it had a cool "feature". Anyone spectating a spectator following a player could click the mouse button, and cause the player's evolve/spawn menu to pop up.
We quickly removed this, but it was fun for a while clicking right as someone ran into a base.