Marrying the ketchups 

The combination of two half-empty (or half-full) bottles of the titular tomato condiment in attempts to make them into one whole bottle of ketchup.
This particular phrase was popularized by the January 25, 2020 episode of Saturday Night Live, hosted by film star Adam Driver.

“I had two half-finished bottles of ketchup and was running out of space in my refrigerator... long story short, my wife walked in on me marrying the ketchups and I had to stop. They didn’t even get to finish their vows, Hank!“ *sobs*

Marrying the ketchups by Sound5cap3 January 28, 2020