I agree, but I would like to add something. If you felt that you offended someone by using "vous", it's likely because this person was the same age as you, and was seeing you as an equal. For example, other students if you're a student, or your direct colleagues (being or not the same age). I think most of the people would just find it funny, but some would actually feel offended. And remember: if you're talking to someone who has the same status as yourself, and you say "vous", the more he/she will find you young or pretty, the more likely he/she will be offended. I've experienced it with a 45 yrs old "colleague" (I was 20 and I was a trainee..). Don't worry too much about those ! Keep saying "vous" to strangers and people you see as superiors. People younger than you will be pleased to be called "vous", and some elders who can't admit they're actually not so young won't. It can't be helped !

I agree with the comment left before me. 'Vous' is truly the safer option to use, as 'tu' can be quite offensive if used to a complete stranger or someone that you should show respect to. However, if someone that you've been speaking to or have a relationship with says that it is acceptable to 'se tutoyer', then you should switch to 'tu.'

"vous" is used to show respect when you talk with a stranger, with someone older than you or with your superiors like a teacher or a boss.