The other person might be referring to Pocky Day and Junko, embarrassed about the romantic implication, deflects by saying it's Spotted Garden Eel Day.
Additionally, the Japanese word for Spotted Garden Eel チンアナゴ (chin-anago) starts with "chin", as does ちんこ (chinko) which is a slang term for penis. So maybe Junko is getting embarrassed about that similarity, and maybe there is no connection to Pocky Day after all.