When Fonzie or another character tells someone to “Sit on it”, what is that person supposed to sit on?

This question has perplexed me for decades. Does anyone know what we should sit on? Sort of vague.

I'm not entirely sure what the HD folks intended others to sit on.

However, in the Middle Ages Vlad Tepes (Dracula's inspiration) DID have folks tortured to death via having them sit on spikes,swords,etc. in the 1400's He went down in history as 'Vlad the Impaler' but I suppose they had to change it to impaling chests instead of backsides for the movies,etc.

We used to say "sit on it and rotate". I'm not actually sure what it meant!!!

It is an old saying as mentioned above. The implication comes from extending the middle finger (more or less universally known gesture) and telling someone to "sit and spin". Where do you think the popular toy from years ago got its name?

Often heard in the military, whiners who are "tired" of drilling may be told by their Sergeant to, "Sit on your finger and rare [sic] back on your thumb!"