The first meaning is that some thinks they are super cool Sauve or just over confident and it turns out they are quite the oppisite. They are just plan full of crap and corny.
The Second meaning is that when someone has no confidence in something they have to or should do and you know they can do it, they are down on themself for no reason that you can see, then they are Yoy, or just plan old looking for attention. Then we add on Bag to make YoyBag a person Full or Yoyness
The third is just a plan old Goof Ball, silly, and you are Enjoying it.
Example # 1 - Like Bill Murray (Something McKraken)in the movie "King Pin" where he thought he was cool and Sauve but, he was Super Yoy, with that Swoop hair did that flowed the other way as he threw his ball down the lane and he thought he was Sexy.....A True Yoy Bag to the highest Level.
Example #2 - When you have a friend that is a really good artist and you think that they have the best talent around and they start doubting themselves. It could be the low self esteem factor or that they really want attention.
Friend " I do not think I should even enter the competition because I will only lose"
You: Oh, Please, you know you have a good chance, you are a Yoy Bag