premise: A construction worker with tattoos on his arms is bending while working, and he is wearing shorts and a blue hard hat. hypothesis: A construction worker drills maniacally into his mother's tombstone.
contradiction: You assume that the construction worker is at work in the first sentence because he is wearing a hard hat and bending down while working, in the second sentence you assume he is doing nefarious things like drilling into his mother's tombstone on his own free time, there fore he cannot simultaneously be at work and off work at the same time.