It's "funny" because sex is taboo in puritanical cultures like the US. Obviously you're not going to use the lube on the Oreo's, but it's funny because by putting them next together, one imagines taking out an Oreo, lubing it up, and then... something? It's unexpected and the mind laughs, even though theres a perfectly normal explanation that doesn't involve those two things being together. Same for adult diapers and baby food. They have an elderly parent and a baby in the house, but the terminally online brain jumps to "it's a weird sex thing".