How do I quit my job? ?

Okay I work at dollar general and I've been working there for three weeks so far. But, one of the guys who works there always insults me. There's another girl, who always catches an attitude with me. She's rude to me and doesn't like me and I've done nothing. Also, my boss is always talking about getting with this girl and getting with that girl even if he is just joking aRound and on top of that, the two youngest girls who work there, smoke weed on the job. Even if it is legal stuff. I'm not comfortable with any of it. I'm going to call my boss today and yell him tomorrow will be my last day. I have another job and I absolutely love it. Everyone is friendly and and my boss there makes me feel a lot more comfortable. My only problem is I'm scared to quit. :( do I just tell him I found something better or tell him it's not the right job for me or make up an excuse and say something like I'm going bak to school full time? I know he will get over it either way but I just wanna get it over with. Help if you can!