Being in a general bad mood, but the spectrum is wide. It can be from simple disappointment or waking up on the wrong side of the bed to utter nihilism and existential angst for the human race, and everything in between. Possibly of Yiddish origin. One who is shtoompy is usually called a shtoomp.
Person: Are you shtoompy?
Shtoomp: What the hell does that mean?!
Person: Don't be such a shtoomp!!
Couples who are constantly feeling the need to be touching, holding hands, kissing, and calling eachother pet names like shmoopy, as if they are forever caught in the state of being a brand new couple that is madly in love. It's from seinfeld
That is the shmoopiest couple I have ever seen. They are always eskimo kissing in front of everyone and it's awkward as hell.