(humorous, imperative, UK) I am about to start a fight.
(humorous, imperative, US) I am about to do something crazy or difficult that will nevertheless be easy for me.
(humorous, imperative, US) I will respond to someone doing something questionable by doing something even more questionable.
Source: en.wiktionary.orgMind you, I've always been musical... Mother used to sit me on her knee and I'd whisper, 'Mummy, Mummy, sing me a lullaby do,' and she'd say: 'Certainly my angel, my wee bundle of happiness, hold my beer while I fetch me banjo.' Les Dawson