In keeping with their brother-sister like teasing on the show, 'The Voice' coaches Adam Levine and Christina Aguilera had some fun bickering on Twitter. Over what? Well, Levine put his foot in his mouth regarding celeb scents -- and Xtina was more than happy to point that out to him.

Levine announced the launch of his upcoming fragrance, 222, last week. Perfectly innocuous and fine, right? Well, yes, until you realize that about a year ago, doing so, by Levine's own account, would be cause for suicide:

Who better to remind him of his own hypocrisy than his 'Voice' rival Aguilera? She clearly enjoyed every minute of it, too, posting a link to his tweet and reminding him of his own remark.

Zing! Aguilera is a perfume veteran, with Christina Aguilera, By Night, Royal Desire and Secret Potion all bearing her name.

While the duo may argue and taunt one another often, they clearly have one another's backs. Levine defended Aguilera to Howard Stern last month when the shock jock grilled the Maroon 5 rocker on her weight.

We think it's so much fun watching the sibling rivalry dynamic at work with these two -- especially when they show that despite their teasing, they're actually tight.