jar = JAR, my initials.
155 is a bit of a story, but I'll condense it down best I can. I used to play soccer, baseball, football, and basketball in competition leagues. In high school I played soccer, football, and basketball. After so many overlapping seasons for so many years, you sort of start to burn out. I dropped all my high school sports except for football, and then only kept on with basketball in the comp league.
The team I was on for basketball was good. Everybody could shoot, we were very athletic, and we were blowing teams out routinely. To make the games more fun, we started doing goofy stuff for fun. We still played hard, but we made pre-game programs to hand out as people came in, we did a halftime half court shot to win something, we got the high school drill team to perform (that pissed some parents off), and we just had more fun in our play, but we still played hard and won. It became a hangout thing, just like regular high school basketball and we would often get 100-200 students there. Other teams complained that we were distracting though, and the league shut down all the antics. The crowds kept coming though.
I still wanted to do something fun, so I took some white tape and added an additional 5 to my jersey, to make it go from 15 to 155. About 3 minutes into the game the ref noticed and just started blowing his whistle like crazy and gave me a technical foul and made me remove the extra digit. The crowd booed like crazy. The rest of the game, any time I committed a foul, the ref would say, "that's a foul on one five" and the crowd would add in a loud "five!" right after. It carried over to the next game, and any time my number was announced, they would add an extra five.
It just stuck. I've been using jar155 online ever since, which is a good 20 years now.