Oh, you better strap in, anon, because I have pixilated stills and poorly drawn visuals. Let’s do this.

Here we have the first known siting of the sinful little thigh tat. He is waiting outside of his old gym coach’s house, plotting to seduce him with his shameful, pasty exposed thigh skin. (1x7 - “Charlie Got Molested”)

Here he is later in the episode, tugging his little shorts up just a bit higher to expose his thighs like a piece of meat for his teacher. Truly a slut move.

The next time we see Mac’s slutty Shamrock isn’t until S3. Clearly the thigh slip is a strategic move on his part to entice the McPoyles into setting the Gang free. (3x4 - “The Gang Gets Held Hostage”) I think we can all agree on where everyone is looking in this shot:

I just realized that both of these episodes feature the McPoyle family. Coincidence???

If anyone can recall other sightings of the Shameful Shamrock of Sin, please let me know!