If a minor character possesses alot of charisma and intriguing characteristics, he/she has the potential to be a bigger character with alot of depth, and that potential is what makes them memorable.
I can think of 5 second characters I love - I just discovered that guy Ogrinn, who shoots the batarian bartender that poisons you if you decide to incite the crowd upon confrontation. If you don't renegade interrupt the moment the bartender equips his gun, Ogrinn shoots the guy like a bamf saying "not taking any chances". Talk to him and he's super snarky and says things like, "I have a ship and a mate. I only brought one of them to Omega." I'd love to see more of that 