1A set expression said after a meal to thank the cook, host, or simply acknowledge the food. Used universally in homes, school lunches, and restaurants. The more polite full form is ごちそうさまでした. Together with いただきます (said before eating), it forms the standard pair of Japanese meal greetings — children learn both as part of basic table manners. Sometimes written ご馳走様, but the kanji 馳 is non-jōyō, so the kana form is overwhelmingly more common.
ごちそうさま、今日のカレー、すごく美味しかった！
Thanks for the meal — today's curry was so good!
ごちそうさまでした、お会計お願いします。
Thank you for the meal — could I have the check, please?
お母さん、ごちそうさま！明日もよろしくね。
Thanks for dinner, Mom! Looking forward to tomorrow too.
今日は奢ってもらってしまって、ごちそうさまでした。
Thank you for treating me today — it was a great meal.
子どもたちは「いただきます」と「ごちそうさま」を必ず言うように教わる。
Children are taught to always say 'itadakimasu' (before) and 'gochisousama' (after) meals.
2A slang/jocular usage: said when witnessing a couple being lovey-dovey, as if you'd been treated to a 'feast' of their PDA. Has a teasing, mock-exasperated tone. Strictly casual — heard in conversation or seen in social media comments, never in formal contexts.
カフェでいちゃつくカップルを見て、友達が「はい、ごちそうさま〜」と笑った。
Watching the lovey-dovey couple at the café, my friend laughed, 'Oh, thanks for the show~'
SNSに新婚旅行のラブラブ写真が並んでて、思わず「ごちそうさま！」とコメントしたくなる。
Looking at all the lovey-dovey honeymoon photos on social media, you can't help wanting to comment 'gochisousama!'