Never happens to me. Because I always make certain to shout out the number of each rep as I'm doing the exercise
Along the lines of "One!!!" "2!!!" and so on
Then if I forget, I just ask out loud if anyone remembers how many reps I did on the last set. They are usually pretty helpful, and often attach useful if unsolicited advice at the end, such as "it was two asshole, and next time add some weight to the bar you pansy ass bitch"
Did I forget to mention that I often forget to add the weights as well? Maybe that's why I always feel so fresh after a workout. I'm gonna have to do something about that, maybe if I write it.....hey whats that?!!
What was I saying?