Saying that u have a headache as an excuse to not do something, avoid doing something, to get someone to shut the fuck up or to get someone to do something.
Example 1
Man: Honey, we have been together for almost six months and i really wanna express my feelings for you physical..
Example 2 Mother: My son went a party Friday night, he played soccer on Saturday and went to the cinema on Sunday but now he says that his head is hurting him and he cannot go to school tomorroe. What a convenient headache..
A: Dude, you look like you're in agony. What's up?
B: I've got a "Mikegrain headache" man. Worst ever. There's a project due next week and he's freaking out like it was due yesterday.
When a woman with a gargantuan hiny sits on your face and gives you a headache from the sheer mass of the ass, it can be said that the woman has a "headache booty"
Man: Dude Alexis and I did some freaky shit last night, I found out she's got a headache booty
Friend: That's just wrong man.