Bench Press or Floor Press with a fat bar or fat gripz.
If you haven't got anything to make the bar THICK you can wear thick gloves too. The idea in this excercise is that you have to SQUEEZE hard the bar.

If you have nothing but a casual bar for this lift, try to lift the bar without squeezing the bar at all, with a flat-grip (palm open, fingers straight) like performing a pushup on the floor.