what would happen if everyone in the world stood in the same place and jumped?

I don't think everyone in the world would fit in the same place at the same time...

The force would be enough to set off a richter scale, but not enough to make more than a tiny wave in the ocean. It wouldn't cause any change in tectonics, nor would it make a difference in volcanic activity. The force of everyone jumping all at the same time is very little in comparison with the mass and density of the earth. You probably wouldn't even be able to feel it if you stoped jumping and stood still while everyone else jumped.

We might cause a little tiny wave on the ocean (unmeasureable). The sheer mass of the earth and its size makes all of humanity seem like nothing.

Though they say that one of those big earthquakes a while back, the Tsunami one.... it made the worlds rotation slow down by like 1 millionth of a second.

Surely not tilt the world off of it's axis, the melting of the polar ice caps will do that.

Absolutely nothing. The earth I'm sure outweighs everyone one the planet.

Might possibly resurerect the Rock group "Van Halen" ?