Green’s Dictionary of Slang

dog it v.2

[put on (the) dog under dog n.2 ]

1. to dress up, to show off.

[US]N.E. Eliason ‘Some Negro Terms’ in AS Apr. 151–2: Dog it: to show off to advantage.
[US]T.B. Haber ‘Canine Terms Applied to Human Beings’ in AS XL:2 95: dog it. To show off to advantage.

2. (orig. N.Z.) to lord it over someone.

[NZ]C.A. Treadwell Recolls. Amateur Soldier 233: There were a good many non-combatant units at headquarters, and many of the non-commissioned officers used to [...] dog it over the men who were across on leave [DNZE].
D. Weil River Home 18: Harv often felt that the veteran mates were trying to ‘dog it over’ him.