Getting wet means smoking or getting high and people usually stand on the corner to do so, regardless of what the weather is. This is also a double entendre because if you are standing on the corner smoking while it is raining you are going to get “wet”.
Also, getting “wet up” could refer to getting bloodied, mostly in reference to getting shot at, but can sometimes be a reference to knife wounds as well. Playing off “wet” and “weather”.
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