Is making fun of someone's pronounciation racist?

A work blogger I respect recently made a joke about their local Chinese takeaway mixing their Ls and their Rs when making a mythical dish. The in-house work magazine recently pointed out a menu slip-up meaning that a dish was described as "Lice" instead of rice, not noting that the two letters are very very far apart on the keyboard.

Naturally, that's immediately raised my hackles and slightly offended me, but I can't decide if it's racist or not. On one hand, people do impersonations of Polish or Birmingham accents all the time. On the other hand, said jokes wouldn't work if you were attributing them to a Turkish takeaway.

Then again, my native-Chinese mandarin teacher habitually mixes up her Ls and her Rs, which rather rankles with me internally. Oh, and the cartoon illustrations in the textbook she uses helpfully distinguish Chinese people by giving them slanted eyes.

*sigh* Oh it's so confusing. But I definitely feel a whiff of genuine offence.