when you go into a store with either,
a) no intention of buying anything
b) no money to buy anything with
just to waste time (i.e. waiting for your friend/a bus/direct deposit to go through)
shlagging can happen unintentionally as well, if one intends on buying, but ends up not purchasing for any reason.
"I wanted that new phone, but they are out of stock, this turned into a shlagging trip."
a person who is blinded by their own false legacy/greatness, usually boastful about things they don't know about or aren't passionate for, but assume others like/want to talk about.
"Fucking majangus over here wont shut up about his new car"
a person who is particularly cantankerous or churlish in the mornings, but not all the time.
Well, I'm glad you had a good day at work, you were quite a grumbledeen earlier.