How to sing with attitude?

I'm in a musical right now that has "lounge singers" singing outside during intermission. I'm one of those singers. I don't have a problem with nerves or anything, but when my boyfriend came and watched, he said I was great but I didn't have as much "sass" as the girl before me. I did all right, I smiled and winked and danced a little bit, but I just didn't have as much attitude as I could have. How can I sing with more attitude?