Ok, so there won't be any neon lights, and the bar selection is not as extensive as in Las Vegas, and the opposite sex selection is not so good too, but the nightlife in the Amazon is one of a kind!
We went on our private boat in the middle of the night to tour the Amazon jungle looking for nocturnal animals. We didn't see our jaguar but we saw other animals.
Our guide even stalked on the shore for a while then suddenly jumped in the water!!! Surreal. When he got up he was holding this baby caymen.
On the boat ride back, I laid down looking right up at the stars thru the jungle canopy. One of a kind nightlife.
Dress Code: Instead of perfume or cologne, make sure to bring bug spray.
If you are looking for a disco in Iquitos, Noa Noa is a good place. It's about 2 blocks off the main plaza downtown. There's a small cover charge, but some of the hotels in town have passes for their guests. There are plenty of singles if you are trying to meet someone. I've always gone with a date, but it looks as if everyone else mingles easily. Don't bother going before 11:30 or midnight. But it gets crowded quickly after midnight. As with every other place I've been to in Iquitos, tourists are welcome there. As far as dress goes, I've seen men in sweats there. I usually wear jeans and a nice shirt. Thankfully, the women dress better than the men.
I entered this bar on my way back to the hostel, as it was one of the few open then. But it happened to be a nice place for a drink and listen to music, with comfortable sofas a a cool atmosphere. I had a mojito and, though it was not specially crowded, had a nice time there.
Rather than plant your butt along the riverfront like other foreigners, just walk around and find a local hole. There´s a fun gay club with a big transvestite scene called (Adonis) 2.5 soles in a moto. There are a couple outdoor venues that have bands on the weekend. Entrance should be 1 or 2 soles.