A: Quiero ir a la casa de Juana a visitarla.
B: ¡Chale! Vamos para allá mañana.
¿Es una ofensa decir "Chale" ?
In your example that interjection doesn't fit quite well. Let me explain.
Concerning Mexico –the only country I've heard this word in, but the range of the usage is often spread by media– it isn't offensive at all. But the word itself doesn't sound very educated: never use it if you are trying to be formal. You could say it or hear it very often in the following situation.
You and your friends are leaving a pub. After paying the bill and giving, say 10% tip, comes the waiter and tells you he wants 15%. You say to your friends:
Chale denotes certain unhappiness, or will to complain by confronting an unexpected situation, and it does so in a very informal way. Dissapointment, in general. But it's way far from being an offense.
Well, now your example: in order for chale to fit there, la casa de Juana should possess an additional meaning, like "casa de Juana" being the name of, say, a pub or A's ex-girlfriend's place:
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No es una ofensa en absoluto, es muy informal, y denota falta de educación por parte del hablante.
En México casi nadie utiliza esa palabra, y si la usas puede que lleguen a burlarse de ti.