Red Flag
Explanation
This comic is about dating "red flags." A woman tells her friend about a second date with a new guy, describing it as "awesome" except that "he threw up a lot of red flags." Her friend asks for clarification, and the woman explains that the man was literally, physically throwing up red flags -- as in vomiting small red flags.
The friend says she does not know about the relationship but that "throwing up red flags is kind of a red flag." The final panel shows the man being confronted: "Don't you tell them on the first date that you love to regurgitate flags, Dave?" and Dave responds "I just have it under control!"
The humor is a classic SMBC literal-interpretation gag. The phrase "red flags" in dating normally refers to warning signs about a potential partner's behavior. By making the red flags literal objects that someone physically throws up (vomits), the comic creates an absurd scenario where the metaphorical warning is itself the literal problem. The meta-joke is that someone who literally vomits flags probably should be considered a red flag in the dating sense as well.