How can one stranger fire me up so much?

I was in CVS with my husband buying light-bulbs. We were play-arguing over the wattage, and as he walked away, I said to him in a loud-ish voice something playful and joking. A woman is squatting below me, complete with her giant Louis Vuitton purse over her shoulder, and says "Ugh (that annoying "ugh" sound) - could you not yell?" so I said "So sorry you have such a bad attitude, that's not my fault." I don't get why, in the midst of having a perfectly good day, some bitch can come along and basically reprimand you for enjoying yourself too much. Nearly 24 hours later and I still want to slap her.