Depending on the level of control the girlfriend exerts, the man maybe designated as one of the following;
1. Sailor Pants
2. Captain Pants
3. Admiral Pants
And the ultimate....
4. Lord Nelson Pants
Alternatively when referring to the individual, his 'Pants Rank' is sufficient;
'Sailor, what time is your Mrs arriving?'
'I hear Alicia moved in and promoted Matt to Admiral... suppose that's the last we will see of him'