Step 1: Impulse-buy a juicy and red quarter of a watermelon.

Step 2: Recall that your friend once served delicious watermelon cocktails. Call your friend and ask him what booze he put in them.

Step 3: Make cocktails as per his suggestions.

Per serving:

• 8 cl watermelon juice (mash up cubes to make juice)
• 4 cl rum
• 1 cl grenadine
• juice of 1/4 of a lime
• dash of bitters

Note: the grenadine (which I own because said friend bought it once to make cocktails when he visited) and bitters (which I own because I bought them once in London when visiting said friend) are both supposedly optional.