(SPOILERS FOR RDR2)
In one of the endings for Red Dead Redemption 2 (Specifically helping John with Low Honor) Arthur gets into a fight and is eventually shot by a former member of the gang,
Micah. During this sequence,
Micah will say *Damn you!" and Arthur will reply with *Damn us both!". The way Arthur says "Damn us both" sounds like "Tennis Boat" which eventually became a
meme.
Micah: "You're not better than me, Morgan!"
Arthur: "Whatever you say, you fool!"
Micah: "Damn you!"
Arthur: "TENNIS BOAT!"
*Arthur dies*