Elton John's Husband -- Cops a Feel of Neil Patrick Harris' Ass!

Please don't squeeze the Neil Patrick Harris.

During a Race to Erase MS charity gala in L.A. this weekend, Elton John's husband David Furnish gave the "Doogie Howser" star a real helping hand ... by copping a sneaky feel of his butt.

As Sir Elton, Neil Patrick and his partner David Burtka posed for pics in a friendly embrace, Furnish tried to get away with pulling the old underhanded ass grab on NPH.

The truth always comes out in the end.