Seeing how you would interpret each icon based on context was an experiment in design.

The last icon is for the "circlejerk": your objective sad face.

This is the part of my reply where i see i should offer more time to collecting hyperlinks for examples, but i hope it follows easily enough:

Relevant xkcd to voting systems: happy button only from me.

Someone saying they got their bike stolen while they were voting: sad button only

Peer-reviewed paper about voting in forums: brain button only

Peer-reviewed paper about the shape of Antarctica: sperm button

Peer-reviewed paper about Maru and the evolution of voting on Youtube: happy button and brain button from me.

Pun threads concerning voting: happy button and the sperm button from me.

Any opinion shared with Caps Lock: sad button and sperm button

Peer-reviewed paper about gun violence and voting systems: sad button and brain button from me.

Any other combinations would defeat themselves, so im don't see any reason to click three buttons or all four. Perhaps the objective votes of brain and sperm are unlocked the way voting is unlocked in AskUbuntu's forums: only after certain contributions and/or circumstances are met.

That's what i'll be fighting for at least. I vote subjectively and i vote objectively. If you make me choose, i'm going for the subjective vote every time. Best to break the two apart.

sperm: Brains have two hemispheres; i wonder if there's correlation....