slip a ginger

To slip a ginger is to take a beverage from the fridge that someone brought over at a previous holiday gathering. The person wasn't expecting to have any of their preferred beverage, in this case ginger ale, at the next holiday gathering, but would've been pleasantly surprised to find one. But they won't. Because you slipped their ginger ale a month before Thanksgiving. They won't notice, of course, having not expected the ginger ale to be there. But it would've been a nice surprise, albeit small. It'll never happen, though, because you slipped their ginger.

It's like shitting in someone's Cheerios, but it doesn't ruin their day, only what might've been, and only slightly.