Simply the combination of both the "lowie" and the "slut", attractive only for sex and thus simply whorelike.
Essentially a code word for males to use in the presents of such persons who fit the above description, so as to keep them unawares.
The SLU comes from the word slut. And the similarity of the word to slurpie is due to the commonality that both slurpies and sluries are so sweet.
"Slurpies are sweet and so is that slurie"
"Wow look at that slurie go"
"How much you think that slurie is?"
"I sure would like to taste that slurie"