The presenter was left out when Gary Barlow, Sharon Osbourne, Nicole Scherzinger and Louis Walsh all received one with their name on during filming today (June 10), as did Xtra Factor hosts Caroline Flack and Matt Richardson.
O'Leary had his picture taken with everyone else's bottles and Flack shared the photo on Twitter, posting: "Dermot is NOT happy..."
The image has been retweeted nearly 500 times.
Personalised bottles are part of the 'Share a Coke' campaign by Coca-Cola.
X Factor auditions are currently taking place in Birmingham, with Sharon Osbourne replacing Tulisa Contostavlos on the judging panel after a six-year break.