He might be lunging out of friendliness. My two boys do this, and it did startle me at first, but they want to be petted. 🙂
Are his ears forward or back? You can make your hand into a small fist, so it looks like a small rabbit head. Place it on the ground off to the side of his head (not right in front of him, as they have a blind spot). If he puts his head down (bunny language for “groom me!”), he wants you to pet him.
I’ve also noticed some bunnies that aren’t sure about you will do this, and it’s half aggressive. But the petting thing works all the same! Then they learn to be aggressively friendly, if that makes sense?
If he’s lunging at you while you are messing around in his cage, that is usually cage aggression, and is common in rabbits that have been caged too much. In that case, try not to mess with his cage while he’s in it. So let him come out while you do any cleaning etc.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.