"The historian Grace Vicary has argued that codpieces were, in a sense, the P.P.E. of their day, born as a means of containing a disease..."

"... in this case syphilis, which was then sweeping through Europe. Treating the French pox, as it was known, called for 'a whole galaxy of herbs, minerals, syrups, and decoctions,' Vicary writes, applied directly in 'a variety of messy unguents and poultices.' If you wanted to protect your fancy wardrobe from stains, the reasoning goes, you would do well to isolate the whole package in an oversized box. Plus, Renaissance men carried a lot of junk on their belts—this was the era that gave us the 'swashbuckler,' after all—and a bit of padding around the crotch would help insulate them 'from bumps and friction.'... [T]he codpiece, designed for discretion, became... a rigid contrivance... 'a permanent erection'.... As early as the fifteen-eighties, Michel de Montaigne had written off the accessory as 'empty and useless,' puzzling, 'What was the meaning of that ridiculous part of the breeches worn by our fathers?'... In the nineteen-sixties, Eldridge Cleaver, a leader of the Black Panther Party, used the profits from his prison memoir to design a pair of pants with a large, 'sock-like codpiece' built in. 'We’ve been castrated in clothing,' Cleaver told the press, 'and my pants open up new vistas. I’m against penis binding.'"

From "Brief History of the Codpiece, the Personal Protection for Renaissance Equipment" (The New Yorker).



That's "Portrait of Charles V with a Dog" by Jakob Seisenegger (1532). Charles V didn't like it and had Titian paint another version of it, which you can see at the link. The Seisenegger has a more prominent codpiece, and it's a sharper image. I prefer it.