Hey buddy, great topic for this forum.
I do not think the waitress was using the word "extranjero" as a derogatory term. It really depends on the word used and the tone of voice/situation.
There are many words used here for "foreigner"...
* extranjero - the most common term and not necessarily derogatory but can be if used in a nasty tone of voice.
* guiri - usually more derogatory and used more often to make fun of a foreigner. A "guiri" is a foreinger that looks and acts like a foreigner (you know, the bermuda shorts and the video and normal camera around the neck

).
* Yankee - Americans and derog. or not depending on the usage.
If a Spaniard wants to insult you he/she will add an explicative to the word like...
* "cabr�n de extranjero" ("cabr�n"="bastard")
* "yankee de mierda" ("mierda"="shit")
* "guiri de los cojones" ("cojones"="nuts", not the type you eat either!)
... but if they just say the word itself, it is not necesarily meant to insult.
Saludos,
jer...