Here are some pointers on how to answer this question diplomatically:

Be Honest: As honesty is usually the best policy, if you have a girlfriend, tell her. Don’t attempt to cover it up or sugarcoat it. It’s preferable to be open and tell her you’re unavailable.

Be Polite: Whether you have a girlfriend or not, respond politely. Thank her for inquiring and expressing your appreciation for her time. This will help to lessen any possible humiliation.

Respectful: If you don’t have a girlfriend, don’t create the idea that you’re looking for one. Instead, inform her that you’re enjoying your present single status and aren’t looking for a relationship. This will show her that you value yourself and your own boundaries.

Don’t Be Too Eager: This, though, might come out as too eager or desperate. Instead, be sincere in your response and allow things to unfold organically. If you’re interested in the woman who’s inquiring, it’s tempting to take advantage of the situation and declare that you’re single.

Be Sensitive: Remember that the girl asking you may have feelings for you, so be sympathetic to her emotions. Do not respond dismissively or casually. Instead, be kind and understanding.