The Andy Griffith Show S04 E30 Barney and Thelma Lou, Phfftt

"Nip it in the bud!"

After an off-hand comment puts Barney in the doghouse with Thelma Lou, he sees her spending her free time with Gomer instead. Not wanting to hurt his friend, Gomer tries to get her to stop seeing him by falsely professing his love, but ends up engaged to her instead.