Just one. I didn't want to, but these natives, I think they were cannibals, were chasing me.
I ran across a rope bridge, and when I got to the other side, I pulled a lighter from my pocket and lit the anchor ropes on fire.
In retrospect, had I pulled out the lighter sooner, disaster may have been averted.
Nonetheless, the natives, seeing the fire start so easily from a device in my hand, immediately dropped to their knees and appeared to be worshipping me. This was fortunate, because I had mis-estimated how long it would have taken the ropes to burn through. They clearly could have made it across the gorge before the bridge failed. 5 minutes later, as the no-longer-restless natives were still bowing before me, the anchor ropes had thinned enough. With a loud "snap", the bridge dropped away from my side of the precipice. I got only a glimpse of the shocked expressions on the native's faces as they plunged into the gorge for several seconds before smashing into the rocks below.
I was happy and lucky to be alive, but saddened when I realized that had I flicked my zippo lighter sooner, their lives may have been spared, plus they might even have bestowed some gifts upon me.
So, yes, I've burned a bridge. Only one.