Can somebody really 'ruin your life' or is it up to the individual's response to a particular situation?

Of course someone can ruin your life; Imagine they maim you, kill your kids, blind you, destroy your reputation with false accusations, infect you with an incurable disease...
There are many things someone can do that will ruin your life, your future, and your opportunities. That's why God invented revenge. Meh.

No one can ruin your life w/out your permission.

However, under extreme circumstances yes, they can help to alter your life, but it would have to be something extremely terrible or heinous, in order, for that to take place such as some form of abuse.

Other ways that people can ruin your life, or at least, try to ruin your life is in relationsihps.

For instance, I have heard of people, who have talked about their ex-girlfriends, or ex-boyfriends when that happened several years ago.

Bottom line: If we'll look to God, then no situation can harm us for the rest of our lives if we refuse to allow it to and look toward God.

I hope this helps to answer your question as that is a very pertinent one to ask!

Parents can ruin their kid's lives with abuse, hatred, unsupportive actions, leaving them to figure life out on their own with no helpful advice or support whatsoever.

I don't believe so. I have always thought that gossip was damaging. However, the people who do it are damaging themselves more in the eyes of anyone who's opinion really matters.

My life just got ruined by other people thinking they know what is best for me. Assumptions led to action led to being affected by their meddling. I can stew on this for another 20 years or accept the fact that it is done and rise above it the way I know how which is all about responsible reaction. I have found great blessings already from this experience because I choose not to blame but accept. It is up to me to handle this lame turn of events in a way that is helpful to others.