This brings back trauma from that black mirror episode…

I feel like a piggyback ride should be a person riding on the back of a piggy, and a piggy back ride should be a piggy riding on the back of a person.

I do like the image, though.

It looks like the etymology is a corruption of “picka”:

https://www.etymonline.com/word/piggyback

piggyback (adj.)

also piggy-back, “on the shoulders or back like a pack or bundle,” 1823, probably a folk etymology alteration of colloquial pickapack, pick pack (1560s) “on the back or shoulders like a pack,” which perhaps is from pick, a dialectal variant of pitch (v.1). As a verb, “to ride piggyback,” by 1952.

Four legs good, two legs BETTER

I like the Jean hat