Germany and Czechia are not surrounding countries but Kaliningrad (then named Královec) was founded by Czech king Přemysl Otakar II. at the height of the Bohemian empire, and was later part of Prussia (basically Germany in the 1800s).
I don’t think many Germans are joking about annexing Kaliningrad because of the WWII stigma but Czech redditors regularly invade r/Kaliningrad only to get promptly banned.