Society has trained us to be persistent and assume "no" means "playing hard to get".
Not so much society, that defers the blame. Women are responsible,
TOO. Every woman that played games instead of just saying "NO, I don't find you attractive and don't want to go out with you."
And, don't get me wrong. Men play games, too.
There nothing wrong with saying no. Count the number of times you said something else to this guy, instead of a direct NO.
Perhaps you've already done this - several times - and the guy just does not "GET IT"
You don't have to lie about STDs or make up boyfriends, just tell him flat out that you don't find him attractive and are not interested in going out. He'll take it one of two ways, get pissed that you don't think he's a 'stud' or 'good catch', or man up and accept that you just don't connect on a level worth pursuing.