When your coworker's defend your honor

I trained someone and he just isn't cut out for the job. Literally everything I taught him went out the window with him. Apparently he has been going around saying I didn't teach him anything which isnt true. In fact I've trained several people who have turned out to be awesome.

Someone asked a coworker of mine how I was as a trainer and they defended my honor and the manager who asked agreed and just thinks the guy is dumb. Others spoke up too and said I do a great job.