When someone says "that's so cheesy," they are usually commenting on something that is perceived as overly sentimental, clichéd, or corny. The term "cheesy" is often used to describe something that is lacking originality or comes across as insincere or exaggerated, especially in the context of emotions, expressions of affection, or romantic gestures.
For example, if someone watches a romantic movie with a predictable plot, over-the-top dialogues, and exaggerated gestures of love, they might say, "That movie was so cheesy." It means that they found the movie to be excessively sentimental or saccharine.
Similarly, if someone receives a love letter with extremely clichéd expressions of love, they might say, "This letter is so cheesy," implying that the content feels insincere or overly melodramatic.
In a casual and light-hearted context, calling something cheesy may not necessarily be negative, and it could be used playfully. However, in some situations, it might be used more critically to express a lack of authenticity or creativity in the expression or behavior being referred to.