Green’s Dictionary of Slang

galloping adj.

[early 17C+] (orig. US) worsening or increasing.

SE in slang uses

In compounds

galloping dandruff (n.) (also crawling dandruff, leaping..., mechanized..., mobile..., walking...)

[1910s+] (Aus./N.Z./US) head or body lice.

galloping dominoes (n.) (also flying dominoes) [domino n.1 (3)]

[1920s–70s] (US) dice.

galloping freckles (n.)

[1920s] (US) head or body lice.

galloping horse (n.) (also gallup) [play on SE horse/horse n. (7)]

[1950s+] (drugs) heroin.

galloping snapshots (n.)

the movies; also attrib.

galloping tintypes (n.)

the movies.