Kate,
to come up with ....can mean....to think of, or invent
A pickup "line" is an introduction that a man uses to attract the interest of a woman when he first meets her.
to come up with a line....to think of something to say when you meet a member of the opposite sex in order to to impress her.
Examples of pickup lines:
Can I take a picture of you, so I can show Santa just what I want for Christmas?
If looks could kill, you would be a weapon of mass destruction.
What does it feel like to be the most beautiful girl in this room?
Chandler probably thought that the woman he was talking with was a lesbian, so there was no reason for him to come up with a line to impress her since she wouldn't be interested in him anyway.