half-glass

v. the act of not filling someone's drink to desired amount.

"Hey bro, get me some vodka."
"Ok, here's some to start."
"What're you doing, dude!? Don't half-glass is it, fill that shit up!"

"Mom, didn't I ask for a glass of Dr. Pepper?"
"Yes, I got you that didn't I?"
"No, you half-glassed it. Can I get more?"