Things Tubby is scared of are; behaving, not barking at nothing, missing a single centimeter of grass to pee on, and lastly not drinking as much toilet water as doggly possible.
In all seriousness Tubby is afraid of loud cars. We live in an apartment which faces a fairly busy street and when the loud cars go by he gets up and starts barking and barking then runs under my feet and gives me the big eyed look
Mabel hasn't been around many things, but she's developing a dislike for the lawn mower and the vacuum cleaner. Our last bullmastiff used to suddenly develop an irrational fear of something that she had been around for a long time. One time she looked up, saw the patio umbrella that had been up all spring and summer, and completely freaked out. We couldn't get her to go outside again unless we were with her and then she'd tuck her tail, duck her head and run as fast as she could away from it.