It is simply impossible to "grow a pair" at the sudden and vociferous behest of others.
This seems like an unassailable proposition. One could, however, make the superficially plausible case that a truly vociferous behest might have some effect on the cremaster muscle, resulting in the rapid descent of "a pair", which might be confused with "growing" a pair. This is not the case. Further investigation reveals that the resulting cremasteric response is more likely to be one of contraction:
Contraction can also occur during moments of extreme fear, possibly to help avoid injuring the testes while dealing with a fight or flight situation.
Where's Matthew Barney when you need him?
The final sentence of hh's comment is frankly baffling. Speaking personally, I have never been tempted to confuse neutropenia and anorchism.