Rouler des mécaniques

Literally: To roll one's mechanics

Example: “Sur la plage, il roule des mécaniques devant les touristes.” — On the beach, he throws his weight around in front of the tourists.

English equivalent: To throw one's weight around

Origin: At the start of the 20th century a solidly built man was said to have something dans les mécaniques — the mécaniques being the skeleton and its joints, which, well made and well covered, make a man look sturdy. Rolling them is the exaggeration: an overdone way of carrying yourself, meant to impress anyone easily impressed. Meant to, only, and rouler said as much itself in the slang of the same period, where it also meant to overdo or lay it on thick, and a rouleur was a talker and a braggart — which is exactly our roller of mechanics.