At one point Hannibal is expecting to be joined by his brother’s army. But on his way, he gets slaughtered. Hannibal realizes his dream of conquest is over when a Roman horseman rides into his camp and throws down the brother’s head in a sack. The questions I come away with are: how was that rider able to ride with such huge balls, and did he get away?
IIRC, Hasdrubal’s head was carried in a sack and then tossed over a wall at Hannibal’s camp. Probably not too difficult to accomplish if the head-tosser looked like an average guy, especially if done at night. He would look like Joe Schmoe with a chicken in a sack. Or a pig in a poke 
Even easier if he looked like this guy.
Seems to me a severed head isn’t going to be in pristine shape under the best of conditions, let alone after having been roughly hacked off with an ancient sword and then bouncing in a sack for a couple of days and a few dozen kilometers of hard riding before then being flung over a wall to land who knows where. After the bag bounced to a stop, how long would it have taken before they knew for sure whose head it was?
Maybe they wrote “hic est frater tuus” on the forehead with a Roman sharpie.
You misspelled “Pugio”
How universal is sack as slang for testicles?
Would Carthaginian or Romans have got the joke or would it have gone down like scabbard/vagina joke in modern English.
The only bit of the Carthaginian language that’s survived is from Roman comedy so we are probably more likely to know about ball jokes in Carthaginian than anything else 
You will be happy to know that sack = testicles = courage is totally classical:
Sed si nos coleos haberemus, non tantum sibi placeret. Nunc populus est domi leones, foras vulpes.