No matter how decent and elegant you are, as long as you refuse others, others will feel uncomfortable more or less. So if there is no one in your heart, you might as well tell him directly. "Sorry, I don't want to find a friend yet!" "I'm sorry, I already have the right person" and "I'm sorry, I'm focusing on my studies now, and I'm not going to think about these problems for the time being", etc., which are all euphemisms.

If you don't want to be friends with others, try not to interact with them when they ask you out:

Ask you out to dinner-I'm working overtime today and I don't have time to go!

Ask you out to play-I'm really tired recently. I just want to lie down and have a rest when I get home from work. Please forgive me.

Invite you to the movies-I've already seen the movie;

I'll call you.-Just mute the phone. Later, when you asked, you replied that your mobile phone was not with you at that time.

All of the above, as long as the other party asks you out three times and you refuse twice, I'm afraid I have understood that there is no hope of making friends with you.

There are many such rejections, and I hope the above can give some inspiration.