Now, as an Italian I can't really say that I am offended by this. I don't care and I frequent the international community for long enough that I got used to the "mamma mia", hand gestures, "mi scuzi" etc., whatever.

That said:

or was a way to hide derogatory behavior

If you don't consider stereotyping people as uneducated half-wits who can't speak a second language and express themselves in super-mario sentences derogatory in itself, I guess you have a very high bar.

Also you kinda made up this definition of prejudice, which simply means having opinions about something in advance.

an unfair and unreasonable opinion or feeling, especially when formed without enough thought or knowledge

Believe it or not, the type of stereotype here represented is quite widespread. Ask any Italian abroad how often they encounter the stuff I mentioned above.

Here, we’ll include Americans in the meme:

The example you bring is then completely off the mark. It's one thing making fun of Italian "society" as - say - unorganized, or something else. It's another thing stereotyping individuals and their individual characteristics.

All in all I have to say that it's quite surprising to see this kind of behavior in the Fediverse, where such behavior would be absolutely not tolerated if it were about some other category. Again, I am fairly neutral and I take the joke for what it is, but the hypocrisy in this thread is really funny.

If Italian people were offended by this

“If” an Italian was, and told you, you’d explain to him he isn’t really offended, like you’re doing now. Because that’s what you are doing after an Italian told you to knock this shit off.