bad....very bad. unclip, pick your bike up and start walking. replacing your cleats would be way cheaper than a new rear weel (or whichever tire is flat). like already suggested, take tube out and run fingers along the inside rim and check. But I have had this happen also. For me it was a matter of being to aggresive with the stem when I was trying to attach my floor pump to it. it happens, just check your equiptment and throw in a new tube.