When you tell someone to fuck off you are showing that they are bothering you on a deep level, because this phrase reflects intense anger and a desire to get rid of the person as soon as possible. If someone makes you upset or angry then you may be tempted to utter this phrase, but take care because you could end up regretting it later on.
Learn to be ok with not being invited, included, or considered.
Don't fuck with feelings, just because you're unsure of your own.
Being a good person does not mean you have to put up with people's bullshit.