At puberty. I noticed mine got darker and more pointy for a bit then got flat again. I think it is the hormones right when you start puberty that cause that.

I think they start and stop with puberty. Some boys nipples get very puffy at the start of puberty but will shrink again. It can be embarrassing for them, can look almost like they're growing breasts like a girl who is starting puberty.

Well as boys do have a small amount of estrogen, they are actually starting to grow breast like girls. But the amount of testosterone produced after the start of puberty will mean they'll shrink back to a normal size. So will only be a small amount of time near the start of puberty if a boy gets puffy nipples

I don't remember getting puffy nips during start of puberty. But maybe I did get it but was too busy noticing my growing penis and pubes and stuff like that to notice lol. I better not get puffy nips now or later. Boobs look good on girls but I don't want them on me lol.

I didn't have boobs, just a bit puffy right around the nipple itself and it was tender. I remember thinking WTF when it happened and asked my mum (who is a doctor) and she just said it was hormones and it will go away. I think Jade's explanation was best about what it is.