Ok this happened after I got home from the grocery store today. Is mayonnaise supposed to do this?

If the tamper seal was intact, it was probably mishandled during shipping/recieving. Someone may have left it in a hot place to allow the egg, water, and oil in the mayonnaise to separate. It could have been a jar that was placed back on the shelf AFTER someone else bought it, left it in a hot vehicle, and returned it to the store. I HOPE that's not what happened, as the store should have disposed of it and recorded it as a damaged product. It happens, and I would have returned it as well.