The term "pack sand up your ass" refers to someone being completely pissed off at someone else. They are hoping and wishing that this said person would experience the most uncomfortable, irritating, violating and very painful feeling up inside their anus cavity similar to having someone pack beach sand forcefully into their rectum.
Jeffery had taken the liberty to take Lonnie's brand new guitar out of the case and try to play it. While fimbling, fumbling and farting around with it with his greasy , dirty, little inexperienced fingers, he broke 3 of the six strings right off the guitar. When arriving home late that night, Lonnie noticed the guitar was missing from the case. Much to his surprize, Lonnie found Jeffery in his pig sty of his room with the new guitar lying in a corner on the floor with the 3 strings missing. Lonnie (now in an extreme state of rage) told Jeffery to "pack sand up your ass" and actually really meant it.
by SkipSpike666 October 21, 2017