吧 here is a phonetic rendering of English "bar" — as in "message bar". Tieba was the dominant Chinese forum of the 2000s-2010s and a major source of internet subcultures (e.g. 屌丝 originated on Li Yi Bar).
A meme referring to mass online raids organized via the Li Yi Bar (李毅吧/帝吧) in the mid-2010s, most famously the 2016 cross-firewall commentary raid on Taiwanese pages.
