means Tasting of salt, or — in slang — irritated, bitter, or resentful, especially over something small.

from Straight from Old English 'sealt,' a word so old its cousins echo across the Germanic and Indo-European family, all circling that same precious crystal. The salty-as-bitter sense is the natural leap — salt water, sweat, and tears all sting the same — but the modern 'acting salty' meaning rode in on 20th-century American slang, likely seeded by sailors' rough, salt-stained reputation and the bitter taste of a sore loser.