People who discovered Lackadaisy because of the pilot (not the comic): I need you to understand that Mordecai and Viktor have a tragic gay-coded relationship that would make this website insane if they weren't literally two silly kitties
Idiomatic: Using, containing, or denoting expressions that are natural to a native speaker."he spoke fluent, idiomatic English"synonyms:natural, native-speaker, grammatical, correct.
Pun: A joke exploiting the different possible meanings of a word or the fact that there are words which sound alike but have different meanings.
So Mordecai is comparing his feelings for this unnamed person to a grammatically correct joke. That plus his expression in the right panel suggest this is a sad admission, that he feels that his feelings are foolish and will not be returned. A perfectly structured cosmic joke.
Trying to get in touch with my shippy side to see if it’ll bring the serotonin back to my brain. They started making out the second that chess board was flung off the table.