“Infamous” means famous in a bad way. It is related to the word “infamy.” Humorists have for a couple of centuries jokingly used the word in a positive sense, but the effectiveness of the joke depends on the listener knowing that this is a misuse of the term. Because this is a very old joke indeed you should stick to using “infamous” only of people like Hitler and Billy the Kid.
“Notorious” means the same thing as “infamous” and should also only be used in a negative sense.
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