love-hurts
Explanation
The Joke
This comic is a promotional strip for the book "Soonish" by Zach and Kelly Weinersmith, presented as a parody of romantic comedy tropes. A woman tells a man named Johnny that she knows he has been in love with her for years, and says she wants to stop lying to herself. She confesses that all the years she thought of him as just a friend or brother, she was actually falling in love. The scene builds to a classic rom-com climax as she reveals she went to a jewelry store, bought two rings, and begins to propose -- "Johnny, will you..."
At this point, an audience erupts with "BOOOOOM!" -- booing the proposal rather than cheering it on. The joke subverts the romantic comedy formula where the audience is supposed to be thrilled by the grand gesture. Instead, the crowd reacts with hostility, as if watching a terrible performance.
The Humor
The comedy operates on the subversion of the "friendzone to romance" trope that dominates romantic comedies. The strip carefully builds every cliche -- the long-unrequited love, the dramatic confession, the jewelry store visit -- only to have the fictional audience reject it entirely. This mirrors the way real audiences sometimes groan at overly saccharine or cliched romantic storylines. The strip is also functioning as an advertisement for the Weinersmiths' book "Soonish," as noted in the bottom panel ("This bonus comic brought to you by buyers of Soonish! Click for info!"), which makes the anti-climactic punchline doubly funny: even the ad itself refuses to deliver a satisfying payoff.