Usually, if you have to ask whether or not you're doing it... You probably are. If you have any doubt, it's best to phrase the statement in such a way that there's no doubt about what you're saying.
The definition of "edition bashing" is a bit subjective, here's how I determine it. (Note: I'm citing specific examples from both sides of the fence because I've seen it from both sides of the fence. Neither "side" is innocent here.)
1) You assert that you play "real" D&D or that you play the game as the designers intended. This usually indicates that the speaker is a big edition basher, especially if they make this assertion when you first meet or play with them.
2) You tell people face-to-face that you're a good player or GM. Although they might just be a goober, these players are usually heavy edition bashers once you get to know them. (It's a bit off-topic, but if you actually tell people that you are "good" at D&D, you're not. People know if you're good at it or not. Just like the clueless guy that's constantly bragging about a sexual conquest, people know that you're full of BS when you do something like this. The people that are legit don't feel a need to advertise it, but everyone loves to hear you make an ass of yourself in public. Sorry, thread de-rail over.)
3) You don't cite actual elements from the game that you dislike, you engage in personal attacks aimed at the player base. The 4E players that do this usually accuse players of Pathfinder or legacy editions of being motivated by "nostalgia," whereas Pathfinder/legacy edition players that do it accuse 4E players of wanting a tabletop video game. If you do either one, I generally consider it edition-bashing.
4) You accuse the game that you dislike of "ruining" the industry. The 4E players used to make snarky remarks about legacy players being "left behind," but that's flipped around these days--now they accuse Pathfinder/legacy players of screwing WotC or "the industry" out of money and weakening the overall hobby by not buying in to their edition of choice. The Pathfinder/legacy people accuse 4E players of dumbing down the game and making it a boardgame/wargame/tabletop video game/anything but a "real" RPG.
5) You assert your opinion as an objective fact.
6) You assert that you speak for all players everywhere, or at least a sizable majority of them.