Breakfast in bed is when one wakes up next to (or happens to come upon) a sleeping lady companion and proceeds to perform cunnilingus on her. This is a gennerally appreciated method of being woken up. The phrase makes allusions to the term "eating out
" as the person performing the oral ministrations is having, euphemisticaly, their first meal of the day in bed. In this case the meal happens to be a woman's genetalia and there is still a need to eat breakfast afterward.
This is similar to, but differs in key ways from, a mongoose
I had great sex with Tiffany last night, so when I woke up and saw that she was still asleep, I had breakfast in bed to thank her.
Lisa I have to call you back, Frank is having breakfast in bed with me. What is he eating? Uh...