put lead in your pencil, on cue

Enhance or restore sexual vigor, as in 

Try one of these hot peppers; that'll put lead in your pencil. 

This phrase, aeuphemism for causing an erection, is considered far more vulgar than the contemporary synonym put hair on one's chest, alluding to a secondary male sex characteristic

Not everyone can cry on cue, even if it would be a relief to be able to. Sometimes there's just a deep "ache," like lead in one's chest.

as if planned to happen exactly at that moment. 

We were traveling up a narrow river in East Africa when, right on cue, a hippopotamus thrust its head out of the water.

 Two years ago, I came out as male-to-female transgender. My wife has come around since then, and our second child will be born before I start my transition.

Because she doesn't like people knowing about her problems, she steadfastly refuses. I'm not sure what else to do. I won't make her stay if she can't handle it, but I refuse to tell her I'll give her full custody