I got no idea - thought it were a clever float idea. Clinton got the same, GWB got the same, Carter got the same. I think even Reagan got the same. All as cartoons, mind, not floats, but it were pretty evenly balanced to both sides.
I am going to be mildly charitable to the woman complaining. She's Kenyan. The last days before Kenyan independance were hard fought, and there was a very bad taste joke going around at the time (I only know it because it was prevalent in the UK about a decade later):
"What is transparent and lays in the gutter? A kaffir with the crap kicked out of him."
Horrible joke, but it might explain her response.