A phrase that one would say in the process of interrupting, upstaging and detracting from another person's shining moment.
Enter unruly nephew: Auntie, those are some great biscuits - I-I'm really happy for you, I'mma let you finish, but Grandma had some of the best biscuits of all time - some of the best biscuits of all time!!
Older lady: You need your ass whipped - go get me a switch!
Dude 1: 'Man this girl was so hot - she had a drink in her hand and was walking over to me at the other end of the ba-'
Dude 2: 'I'mma let u finish, but she was the ugliest girl of all time!'
Dude 1: Thanks, douche.