Learn English – Idiom / phrase for a treasure in a ruin

To stay one's hunger is perfectly acceptable, and not at all uncommon (though it's actually more likely to be "stay your appetite"). Less common, and with less of a "temporarily" sense, would be assuage one's hunger. But I think probably the most common idiomatic usage is...

Here - have a sandwich to stave off your hunger until dinnertime.

...which my mother used to say to me when I was a child. Perhaps this one gains traction by alliteration / association with both stay and starve.

to stave off
to fend off, to ward off (something adverse) _{Merriam-Webster}

(To metaphorically repel / drive away using a stave = staff = stick.)

In English, we have the infamous know-it-all: one who knows everything; hence, a person who makes pretension to great knowledge, especially one whose didactic conversational habit conspicuously reveals his belief that he has superior knowledge on many subjects; a wiseacre; a know-all; -- usually ironical. [Colloq. & pejorative] Note: the use of this term implies that the speaker disapproves of this behavior, and may think that it is unjustified.

**know all: someone who seems to know everything and annoys other people by showing how clever they are.

No one likes him because he's such a know-all.

smarty-pants is an older idiom, for one who is obnoxiously self-assertive and arrogant, as is weisenheimer.

There is the Jerkass, who might say something like, "Sometimes I park in handicapped spaces while handicapped people make handicapped faces. I'm an asshole!" (— Denis Leary, Asshole) but this is more trope or jargon.

And, as StoneyB has kindly reminded me, there is the loudmouth:

Be loquacious, often noisily or boastfully; someone who talks too much or too loudly, esp. in an offensive or stupid way

*Harvard Square: Know-it-all capital of the universe. * - Universal Hub.