If you're not interested you say "No." pause and walk away.
If you ARE interested you can say alot of different things lol like:
"You know I'm not sure... here, walk by one more time... yeah i do believe in love at first sight"
"I dunno... do you? should i walk past again?"
chances are if she's lame enough to use a line like that 1. she's desperate... cause when do girls use a line like that? 2. your clever response will win her over for the night... which can be good or bad.
please see thread "6GA Life Experience: How to deal with the results of impaired judgement brought upon by light to heavy substance abuse"