Max's favorite bar is a recurring event that implies that any bar that Max loves will be destroyed. It is an homage to Imperative, one of Xetaja's roleplays. It is a common plot device used in Route 50 lore to portray staff as ordinary members, humanizing them instead of deifing them.
The bar originated in the roleplay Imperative, which was primarily dominated by Sparky's RP generation-- Kat, Xetaja, Sparky, Max, Navarr, et cetera. As such, the exact details of the roleplay are not well known.
However former roleplayers acknowledge that Xetaja's character was the bartender, and the establishment was destroyed by a hand grenade of some sort. It is not confirmed whether Max, his character, or both loved the bar.
Max, Navarr, and Xetaja were chatting about Imperative on the night that Pokemon to the Rescue finished. Due to entering the chat partway through the conversation, players from PttR were quick to integrate the destruction of Max's favorite bar into the mythos and lore.