Someone who can't stay up past 12:30 AM because they lack the ability of being "awesome". Usually falls asleep after this time immediately or has some type of excuse, ex. I have work at 10 in the morning, I need sleep.
The mcweak refers to the person taking the insult, and the weaksauce refers to being weak, insufficient, puny, pathetic, or even at times saucey.
"Man, Taylor and Jordan should make a club called Weaksauce Mcweaks united, they apparently can't stay up past 12:30."
"That guys such a weaksauce mcweak, who works at 10 in the morning?"