To combine or serve a food item with ketchup, often implying an enthusiastic or excessive use of the condiment.
Figuratively, to unite two dissimilar or incongruous things in a way that seems oddly matched or humorously incompatible.
2.
Regional or niche usageslangregional
A playful or ironic expression used to describe adopting a commonplace or populist addition (the 'ketchup') to something perceived as otherwise refined or unsuitable.