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..
The headach onegets from working with someone named Mike.
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.
The headache following playing a video game for a long amount of time. This originates from the game Assassin's Creed II in which the main character is put into a machine called the Animus which allows him to relive the memories of ancestors and towards the end of the game, experiences some side effects such as headaches and hallucinations.
Guy 1: Hey wanna go to a party tonight
Guy 2: Sorry dude, i just spent 8 hours straight playing MW2 and have the worst animus headache.