A “Dad Sandwich” is when a person who is usually smaller in stature, such as a small queer male or small woman, is caught between two “Daddies” or older dominant men during sexual intercourse.
Brian: “I met these two daddies at the bar. I got a Dad Sandwich if you know what I mean,”
…
Jessica: “I met up with these two daddies last night. I was the meat in their Dad Sandwich”