Said casually while commenting on some brother v. brother or daughter vs. father feud, intra-tribal war, etc.
"Yes, it is truly sad. Family conflicts are always the most bitter. That's why our dwarven friend here hates goblins so much..."
Before the session, ask DM to hand you a fake note sometime during the game. Read it, and regard the dwarf player with a look of pure horror: "Green Slime! [or your ooze of choice]" Allow party to react for a few seconds, then look again and say "Sorry everyone... my mistake. It's just a bit shocking to realize exactly how rare it is that a dwarf and a bath have the pleasure of becoming acquainted."
"Dwarf! We need you to open this door. ... No, no, no. Put the axe away. Good. Now, then. [*mime reaching down to remove his helmet*]. Okay, everyone, we've got our battering ram!"
After a battle in which the dwarf has performed particularly well: "Yes, centuries from now, I'll be able to bring your grandchildren to this spot, and tell them of your triumph here today. 'Kids,' I'll say, 'Do you see how all of these skeletons have broken kneecaps. You grandpa did that."