Be Prepared Meaning

(euphemistic) To be prepared for a sexual encounter by carrying or possessing condoms or other means for preventing pregnancy and sexually transmitted disease.

Example: Used other than as an idiom: see be,‎ prepared.
1963, Margery Allingham, chapter 20, The China Governess[1]:
  The story struck the depressingly familiar note with which true stories ring in the tried ears of experienced policemen. […] The second note, the high alarum, not so familiar and always important since it indicates the paramount sin in Man's private calendar, took most of them by surprise although they had been well prepared.
(This entry is here for translation purposes only.) To always be in a state of readiness in mind and body to do your duty (motto of the Boy Scouts and pioneers).