I'm worried about getting herpes.
Don't you use protection during sex?
Sometimes, I'm just worried about getting AIDS and other venereal diseases
You should get tested first before sleeping around. Ask the other person about getting tested also. It is better to be safe than sorry.
I don't want to deal with STDs, I just want casual sex.
There's nothing wrong with having casual sex with a consenting partner, but it is good to take measures to prevent against sexually transmitted diseases. Just make sure that you're using protection and that you and your partners are clean.