It may not be a great idea to say this around U.S. Marines, as they are also called devil dogs; the easy going ones probably won't care, but you may get punched in the face by the homophobic ones who don't want anything to do with sharing a nickname that is also used for a form of anal sex.
Person 2: Cool man, props for devil doggin' it!
"Hey there devil dog, you keep shooting like that and there won't be any enemy for the rest of us."
1. Commonly used to address another Marine and has no real negative connotations (unless spoken sarcastically, at which point the speaker is likely to spring a rather nasty leak).
2. Used to address a Marine who's name is not known (before nametapes on the utility uniform became standard).
"Hey Devildog, what unit you with?"