Defense, excuse, explain, rationalize. Its from the book No More Mr. Nice Guy. Typically when a man is so ingrained in his wife's frame, that he's scared of her emotions, that whenever he wants to do something, he has to DEER.
Example: Baby I'm going with the boys to drink and talk $hit, his wifes gets upset, then guy proceeds to DEER "But baby its being a while since I've gone with the boys" or "Baby it will only for 1 hour" or "Baby I want some time with the boys"
Its a form of being afraid of rocking the boat, that the guy thinks the wife or ltr will leave him. But it can be related to everything, when you try to explain something y being afraid of consequences.