I can’t remember mine and my mom never mentioned it, but my son’s was “teeth” and he pointed at them when he said it. He then learned words very rapidly and never went through the “phrase phase”. Before he could walk, my neighbor and I were making chocolate truffles and smelled it and all of the sudden, popped out with: “Gimme some of that, gimme some of that, gimme some of that CHOCOLATE NOW!!!”
My favorite is my niece’s. I was giving her a bath as a very small baby and my sister had showed me how she would soap her back up and then draw daisies on it. She would then tickle her and say the word tickle. I did the same and she giggled back and said “ticko”. My sister (fortunately) heard it from another room and came running and my niece kept repeating it for her.