I think the general negative stereotype about Spaniards in Mexico is that they're brash and stupid. Mexico's negative Polish jokes demeaning a culture's intelligence would be comparable to Galician jokes, dating from a time when there used to be more Galician immigration into Mexico. Iberian accents don't sound cultured and distinguished to most Mexicans; also, Spaniards more casually use words that sound rude to Mexicans or use words with different general meanings like "coger" ("take" in Spain but "fuck" with sexual meaning in Mexico). It's a funny situation not comparable to how most British accents sound cultured and distinguished to US nationals.

On the other hand, Mexicans use more diminutives compared to Spaniards and have lost the informal plural "you", always using what would be the the formal form of address in Spain. Mexicans often also say "¿mande?" to acknowledge you or request that you repeat yourself, but this more literally means something very servile like "order me" or "what is your command?", a remnant of the Spanish conquest of Mexico. For this reason, Mexicans sometimes sound excessively polite to Spaniards.

Of course, these are just broad stereotypes and it's entirely possible that pier25 has not experienced any of this. Possibly simply due to being foreign and the generally unacknowledged racism we have in Mexico (white is pretty), pier25's experience may have been entirely positive.

Also, pier25 may look like a gringo but he's not a gringo. In Mexico, only people from the US are gringos, regardless of their appearance. Obama is a gringo; Trudeau is not a gringo (other countries use the term "gringo" differently). As soon as pier25 speaks, no Mexican would call him gringo. Gachupín is an older somewhat pejorative term for Spaniards in Mexico, but I think it's rarely used nowadays.