Usually "the new Spring line" refers to the new selection of clothing each fashion designer debuts during Spring. However, a "line" can also mean an attempt at witty conversation that a man will use to try and pick up a woman at a bar.
For example, this would be a "line": "Hi there, pretty lady. Are your feet tired? Because you've been running through my mind ever since I saw you."
So the cartoon is sort of incorporating both meanings of the phrase to make a joke.
Student or Learner