I realized just now that a lot of people outside Poland don't know about the mayonnaise conflict. It's an ongoing feud between fans of Winiary (currently a brand owned by Nestle,) and Kielecki (manufactured by a co-op).

The feud reintensifies during holidays (Christmas and Easter) when the vegetable salad is usually made in large quantities. The seriousness is at the level of Amiga vs. C64 feud. So some people take it too seriously, some don't so we get this: