A photographer gifted with reasonably sophisticated equipment but poor judgment and social skills, often also with mediocre (or worse) photography skills, who takes great pleasure of making an ass of himself not only in public but among other photographers. A DoucheSLRbag will approach you in public, not to be friendly, but to offer his critique on why he thinks you're not going to get good photographs. A DoucheSLRbag will also make use of Internet forums and social media in an attempt to call attention to how much better a photographer he thinks he is than others, but more often than not does a better job of calling attention to his own shriveled and shrunken skills in the field.
I was trying to take snapshots at a performance and some DoucheSLRbag interrupted me to tell me I'm doing it all wrong and with the wrong kind of camera.