I’m Chinese and I can safely say that many Asians aren’t aware of the concept of blackface. You can argue that it’s the 21st century and the era of globalization but the truth is, Asian culture is quite cloistered and many don’t recognize western perceptions of racism (or racism at all actually). I’d also like to point out that this comic is fan-translated and was never meant for a westernized audience, which is why the author was quite amiss when they made this decision. Yes, blackface is terrible but I don’t think the authors were quite aware of who they could have offended by doing this. Hopefully they will be aware in the future in people message and patiently explain to them.
I’m lucky enough I never had a groupmate who really slacked off (incompetency maybe, but not absent entirely). The only time we had a slacker we dedicated a slide to him calling him a monkey who was busy swinging from tree to tree and humiliated him in front of class. Teacher was not happy.