You might as well tell the truth because saying "I have a boyfriend" does not stop a lot of dudes. They'll just hit you with the "well, you can't have a friend?" line.
Not to mention, for some women, saying "I have a boyfriend" isn't necessarily a code for "I'm not interested." For some, it's more like a "well, you've been warned just in case he stalks you and jumps you one morning when you leave your driveway for work after finding your texts in my phone" code.
But how would this scenario even come up with someone you just met? Dudes asking for dates before numbers now?
If you gave a dude you met your number, and he's not a co-worker or providing some kind of business for you, then he's going to assume you're interested. So, he's going to ask you out. So, you shouldn't even give a dude your number in the first place for him to ask you out unless you are interested.
This is why dudes need to step their game up and give a chick their number and let her call you. Chicks give out their numbers for all types of attention whore reasons.....with NO INTENTION of ever going on a damn date. They just like having their phone buzzing every few minutes with some knucklehead telling her "good morning." Dudes think they "bagged" a chick by getting her number at the bus stop when they all they did was "bag" a text inbox.
But dudes won't do that....dudes afraid the chicks won't call. Well, clasp your right hand with your left hand, raise your head to the sky and say "Thank you, White Jesus" because those chicks weren't interested anyway and they just saved you some time and data usage.
But the chicks that DO call are very interested and are down for meeting up. Leave the gameplay for Parker Bros.....guessing games not included.
Peace