Men who show signs of being particularly pushed around by their senses (sensuality, broadly considered, but certainly including sexuality) or by their emotions, ones lacking sturdiness of character, ones with fragile bearing, excitable types.

A well lived priesthood is very demanding, requiring "white martyrdom" hourly, and sometimes red martyrdom. 

In the words of St Paul and in the final words of the Mass today priests should always be "carrying on in them the dying of Christ".