When you are feeling not really happy but not really sad. Maybe under the influence of antidepressants.
Adam: Hey Fred how ya doing
Fred: Meh, so so just surfing the line.
surfing the line V. Under the effects of some anti-depressants. You are not really happy and not really sad. You are surfing the line between.
Hey Fred how ya feeling today. Meh so-so I'm just surfing the line.