Nemo me impune lacessit (also spelled laecessit) is the motto of the Black Watch, Royal Highlanders Regiment, of the British Infantry. In Latin, the motto translates to "No one attacks me with impunity," or in the vulgar, "Mess with me and I'll kick your ass."
The motto is deeply reflective of the Regiment's history, and like the Black Watch themselves, it is a powerful symbol of British Imperialism.
The Black Watch were officially formed in 1715, from among the Scottish clans loyal to King George I. The men of the Black Watch had already been serving Britain informally for decades, helping to enforce the crown's dominance over Scotland. Joining the watch was quite attractive to the young men of good breeding in the Highlands, since membership carried with it the privilege of bearing arms; in order to secure Britain's domination over Scotland, George I had outlawed the bearing of arms by individuals in Scotland. Only government-sanctioned troops were allowed to carry swords - the famous Scottish claymores were banned and anyone caught carrying them would be expatriated.
Over time, the role of the Black Watch expanded beyond simply enforcing the King's law on Scotland. In 1743, the regiment traveled to the Continent to enforce Britain's interests there. They caused quite a fashion stir, as they were the first kilted regiment seen outside Scotland. Their famous dark blue and green plaid is still commonly worn today, incorporated into a wide variety of fashions.
The Regiment went on to distinguish itself in the Americas, in conflicts with the French, and over the years has played an important part in the major conflicts in which Britain has fought, including both World Wars.
The fame and reputation of the Black Watch have inspired many other organizations, who have adopted the Scottish thistle and the famous Latin motto for their own.