"Guinea" is a slur.
"Pig" is an insult.
But "Guinea pig" is a cute little pet.
Or a cute little pet name for your Italian chauvinistic boyfriend.
Or an experimental test subject in an experiment that you're conducting on your Italian chauvinistic boyfriend.**
Perhaps making him run through a maze.
** Especially if you're dating a cute little rodent.
Conclusion of experiment: date a rodent, not a chauvinist.