They were friends when suddenly...?

[MothMantras]

I hand raised a female bearded dragon from a baby and she is now about a year old. I recently bought a male that is about 10 months old. I introduced them carefully and warily and they got along perfectly, no signs of stress pf aggression from either of them and they generally seemed to not care about each other. I was holding the female yesterday when suddenly I looked at the male in his enclosure and his bear became pitch black, he got a ton of stress marks and he began head bobbing at her vigorously. Today I had her out and while his beard got a bit darker he did not act nearly as aggressive and he did not head bob at all. What is with the sudden hatred and then somewhat more docile behavior? They were getting along so well...

 

[Rampagingraptor]

Beardies are very solitary animals, and they tend to sometimes get territorial.
However, this sounds more like a mating display. Male beardies head bob and black beard when they are trying to impress the female as well as for dominance.
Stress marks is a misnomer, so many things can create those patterns, such as being cold. I would avoid using it as an indicator of stress at all.

 

[kingofnobbys]

Teenagers !!! rampant raging hormones are to blame .... he wants to mate, she's way too young to be mated.

You are in for a torrid time with your little boy for a month or so. Expect lots of BBing, headbanging, nutty behaviour and embarrising behaviour in public from him ,and loads of arm waving and headnodding from her.