Jarring means collecting your bodily waste and/or fluids (generally describing urine or feces, but also includes sperm, blood, phlegm, pubic hair, boogers/snot, earwax, puss, those little tails that come from blackheads, fingernails, and nut-butter) in a small jar. Commonly practiced by psychopaths and the extremely lazy. The lazy hide their jarring from others (usually under their bed) and psychopaths jar for many years and display their collection(s) proudly on shelves.
Dude, my girlfriend told me that she has been jarring for the last two weeks! Yea... I broke it off... quickly.