What does "I've been Boo'd" mean?

What does "I've been Boo'd" mean? I've seen it in several posts over the past few days.

http://petoftheday.com/talk/showthread.php?t=114923 See there ;)

Its a surprise! :D :)

Other thread

Can we beg for the truth on this thread, too?

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Originally Posted by GreyhoundGirl

Can we beg for the truth on this thread, too?

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Hehehe no sorry you will have to be patient until you get Boo'd too :P (I'm certain you will)

Quote:

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Originally Posted by cassiesmom

What does "I've been Boo'd" mean? I've seen it in several posts over the past few days.

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I just got boo-ed too!