So, for the record:
Some people like to use phrases like 'Blessed Be', 'So Mote it Be', 'Merry Meet', and 'Merry Part', when talking to other pagans online. However, don't be surprised if someone asks you not to, or might possibly be offended by your doing so.
These phrases are ritual language. That is to say, they are phrases used within the structure of Wiccan ritual for very specific purposes, and outside of that context they may be meaningless, or incorrectly applied. Some Wiccans feel that using them out of context cheapens or degrades their sacredness. Others may not feel as strongly.
'Blessed Be' is a very specific blessing. It's not a greeting or a parting, and by using it as such you're showing you don't know what it means, or that you don't value its' importance to Wiccans.
Also, amongst initiated Wiccans, there is very much a feeling that people who pepper their speech or writing with these phrases are trying hard -too hard, really- to fit into a subculture they feel insecure about. We all know people who overuse the jargon for certain groups or interests in order to look experienced or knowledgeable...but quite often it's too much the other way, and you end up looking like a noob. My own experience as a Wiccan has been so.
There's nothing wrong with just talking to other pagans, or specifically Wiccans, like you would anyone else. "Hi" and "TTYL" work just fine, and they're not going to upset anyone or make you look over-enthusiastic.
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It's ok to not know these sorts of things. Valid, factual information about Wicca, and especially Wiccan practice, can be very thin on the ground for non-initiates. But once you do know the
facts, there's no reason not to act on them.
If you're asked politely to stop using these ritual phrases out of context, please do so out of courtesy. It's greatly appreciated.