Define Feeling Blue Meaning

I was really feeling blue after she told me she was leaving.

I was feeling blue when after I woke up from bedwetting, and then started to sob even after I snapped of my wet pjs, due to that my Wet Boy's Fruit Of The Loom Blue Stripe Decorative Boxer Brief Undies were still on!

"feeling blue? try to feel red!"

oh look at blue, blue feels