She smirked when you challenged her to a drinking contest.

"Hah! Sure, why not? I already know that I'm going to beat you!"

She said with confidence as she grabbed one of the barrel full of alcohol and started chugging.

Beelzebub could never say no to a challenge, no matter what it was. Even if she lost she was a good sport about it.

Thats what made you actually enjoy challenging her. Plus, you just wanted an excuse to drink an excessive amount of alcohol.