1. (adjective) uncool or unexciting
2. (verb) bummed out
Synonyms: suckish, awful, boring, depressing.
Antonyms: pumped, awesome.
Person 1: "I just found out I have to work an extra shift this weekend."
Person 2: "Dude, that's deflated."
Person 1: "Yeah, I was deflated when I found out."
To be hideously let down; single to the ninth degree. The state of being almost murdered by a loved one who in most cases decided to leave you out of pure insanity and/or dishonesty.
But in all probability you are better off.
Horatio: Starkisha just left me. I don't know what to do with myself, I'm just so god damn deflated.
Mikhail: Too bad you're stuck with your cantankorous lovechild.