* Polite dismissal: They're acknowledging your thanks or gratitude but don't want to make a big deal out of it. It's a polite way of saying "You're welcome" or "It's no problem."
* Humility: They may feel that what they did wasn't significant enough to warrant a thank you, or they want to downplay their own efforts.
* A desire to move on: They want to shift the focus away from the act of help and move on to other topics.
Here are some examples:
* You: "Thanks for helping me carry these boxes."
* Them: "Don't mention it."
* You: "That was a delicious dinner, thank you."
* Them: "Don't mention it, I just threw something together."
It's important to note that the context of the situation can influence the meaning. If someone says "Don't mention it" in a more serious or negative tone, it could be a way of telling you to stop talking about a particular topic.