Most intimidating military uniforms
They had made it a point in their honour code to be the most scandalous, womanising, daredevil of all military corps. British actor David Hemmings totally owned the look in the 1968 film Charge of the Light Brigade.
These armoured lancers wore large wings on their backs, in order to intimidate their enemies with the sight and sound (the rattling of the feathers) as they charged.
I would say one of the most intimidating and scary uniforms were part of the Ottoman Empire army. They were sent to the frontier to harass troops and cause havoc before the regular army arrived.
They were pretty much a bunch of psychopath thugs that were hired to commit atrocities.
Everyone has seen this painting, by Theodore Gericault. That dashing fellow charging on his horse is a hussar.
(edit: no it isn't, see comment by : a short fur edged jacket which was often worn slung over one shoulder in the style of a cape, and was fastened with a cord.
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A The best implementations in my humble opinion are the classic Hungarian green/red outfit and the regimental outfits of Napoleon's army (ca 1812).