Why does ds (8) need to be excessively silly when dh and I are together, but can be fine when with only one of us?

[clumsymum]

Evenings and weekends are becoming really trying, because ds seems to need to show off/get silly all the time, when dh and I are both at home.

When I pick him up from school, he'll be fine, chatty, even helpful.

When dh walks in at about 6:30, ds will become silly and deliberately annoying.
I know it's a form of attention seeking, but
a) we don't immediately ignore ds when dh comes in, and
b) his silliness makes it very difficult to do anything as a family, such as watch a film/play a boardgame etc, because dh and I get exasperated.

DS can't explain it.

Oh and it does happen the other way round, when I go out and leave them together.

Any ideas, cos it's driving us scatty.

Clumsymum - I feel your pain. My boys are like this the DH minute DH walks throught the door.

I have no advice to offer but we leave any grown up chat for when the little monkeys are in bed.

wait till he's 11 or 12 and skulking in his room rather than interacting with you.

oh Backfire, that makes me feel quite sad.

he can be such good company on a 1-to-1 basis.