It's crystal clear, Gwen Stefani and Blake Shelton haven't lost that flirty playfulness they've had with each other since they began their very public romance in 2015.On the heels of Shelton's blunder, where he mistakenly said 'say stace' instead of 'stay safe' after their performance during Sunday's ACM Presents: Our Country special, the Don't Speak singer couldn't resist poking fun at her beau.Stefani, 50, has since taken to Instagram and shared a clip of the mishap with the caption: '#saysace Gx @blakeshelton.' Flirty fun: Gwen Stefani couldn't resist teasing Blake Shelton for 'stay safe' mishap during their 'ACM Presents: Our Country' performance on SundayShowing he too could laugh at himself, the country crooner followed up his.