Here's why:
* It ends in a consonant: In French, most nouns ending in consonants are masculine.
* It's an adjective: While not always true, adjectives in French often have the same gender as the noun they describe. So, if you're talking about a "drole de personne" (funny person), "personne" is feminine, but "drole" remains masculine.
Here's an example:
* Un drôle de type: A funny guy (masculine)
* Une drôle de dame: A funny lady (feminine)