a trigger is anything that makes a person feel uncomfortable, upset, scared, frightened, highly emotional...

examples

some people cringe when they see a spider for them spiders are a trigger.
some people feel uncomfortable when someone compliments them. for then compliments are a trigger.

I have a fear of heights, for me high places are a trigger.

an example of when a trigger came from no where with me was when a friend sat down next to me at a dinner party. she never hurt me in any way and I had no idea the perfume she was wearing was on that I was allergic to. all of a sudden there she was next to me asking if the chair next to me was taken and as she sat down I felt very uncomfortable. it was only after I excused myself to call home and check in with the sitter that I realized this really close friend of mine was wearing perfume when she normally did not.

most people have what is called personal space, its that area around your whole body, like for about 8-12 inches of space between each other when near people. sometimes it doesnt matter, if someone invades that personal space it can feel uncomfortable or upsetting,

my suggestion is maybe next time you get this feeling you can let your father know it makes you uncomfortable being touched sometimes. maybe you can set a personal boundary of asking people to ask you before touching or hugging you. most schools now starting with preschool teach children to ask before touching someone and having others ask them before getting hugs and such. So it wouldnt be anything out of the normal in you asking people to ask you first you can just tell them something like its something you learned in school and are now going to give it a try but remember if you want others to ask before any touching you will also need to do the same. teach by example ...