Intrusive thoughts are disturbing thoughts that occur to you randomly. For example, if you're on a high ledge, you may randomly think "You should jump now", or in a meeting, you may think "Yell a swear word!"
These thoughts are perfectly normal, and do not reflect on you at all. It is actually a very normal part of the brain, and a 2014 study showed that 93% of people regularly have them.
To battle them, mentally label them when they pop up. Remember, these thoughts do not mean you are a bad person. You are not your thoughts. Dwelling on them will only make it worse.