I believe it is vital we control our thought life. I have read many times that "thoughts are things." I agree with DEQ about some of the awful deeds that have resulted from bad thoughts. That being said, I believe it is NOT okay to have bad thoughts.
I have found idleness is where the bad thoughts can creep in, or when someone has been nasty,(I picture myself telling that person off)... Also I tend to start dwelling on it, stuff like that.
Here is what I do: I try to get a good night's sleep. Sleep deprivation lowers my tolerance, and negative thoughts can escalate...little things that would not normally upset me can turn a molehill into a mountain.
Also, I leave the house to change the energy. I call this POSITIVE distraction. I read inspirational books all the time which keeps positive energy on an even keel. I also go to a funny movie. Laughter is one of the most wonderful things to get caught up in.
Staying busy doing what I love or working on a positive project (I love going through old pictures and putting them in an album) or creating beautiful greeting cards, writing a positive letter covered with great stickers...all this keeps my mind positive...not to mention calling someone to brighten their day or purchasing a gift for someone you love...just because....
Just before bedtime, my husband and I always watch a comedy, which is a great way to end the day.
Another way to control negative thoughts is to keep very busy: Action Absorbs Anxiety...just leave the house and run, run, run, or walk, walk, walk and take in nature.
I hope this helps and thank you, KeithJK, for a great question... Blessings, Sparklea :)