Mehdi fell asleep in his chair today, so Roger thought it might be a good idea to take advantage of his narcoleptic episode and give him an unwanted tattoo.
If you're wondering why he fell asleep without his T-shirt on, that was a pure coincidence. Also, Roger having all the stuff ready for the tattoo was purely coincidental, aswell as Mehdi waking up exactly just when the tattoo was done.
Boy! Talking about a weirdly coincidental day!