When a girl says, "I am messing with you," it means that she is playfully teasing or joking with you in a lighthearted manner. It's a way of saying that she is not being serious and is just having fun with you.
In this context, "messing with you" doesn't imply any negative intentions or harm. Instead, it's often a sign of comfort and familiarity between friends or people who share a good rapport. It's a way of injecting humor and creating a playful atmosphere in the conversation.
If someone says this to you, it's usually an invitation to join in the fun and not take things too seriously. It's essential to understand the context and tone of the conversation to gauge whether the person is genuinely joking or if there might be more to their statement. Always be attentive to nonverbal cues and the overall dynamics of the interaction to interpret the message accurately.