Well, who's your favorite boxer? How about Sonny, Ali, Mike, Tyson, or a generic Champ, Slugger, or Punchy. Female names could be Ringer, Laila, Momo, Anna, or Dakota. Have fun!
In general dogs name are so repetitive so I understand that it can be difficult to yo choosing a name for your dog. But afortunately for you my boyfriend has a boxer with a very original name. So my advise is to call it Friky.
