wuss out (of something)
slang To withdraw from doing something out of fear, insecurity, or laziness. They were just about to strap me in for the bungie jump, but I wussed out at the last second. Jeff had promised to help, but he wussed out of the project when he realized how much work it would entail. Sorry, guys, Janet's wussing out of the road trip. She says she isn't comfortable being away from home for that long.
To withdraw from a commitment or course of action because of cowardice or insecurity: I was going to go into the haunted house, but then I wussed out and stayed in the car.