Uses of tu and Ud.
Back in high school, I was taught that in Spanish you use tu to speak with friends and family and you use Ud. with everyone else, and that Ud. was a form of respect. However, I've seen (heard) tu and Ud. used in various ways that to me don't quite fit that rather broad explanation. Following are several examples:
- On a telenovella, a woman used tu with a man she didn't know very well to let him know that she wanted to be intimate.
- In a book, a chief of police used tu with his subordinates while they all used Ud. with him.
- When praying, tu is used, despite the fact that it would seem to require the ultimate form of respect.
- In a movie, a group of thugs used vos with a man they didn't know as a form of intimidation.
- A father switched from tu to Ud. when he got angry with an inattentive child.
What are some other usages of tu and Ud. that don't fit the basic school definition?
4 Answers
In a book, a chief of police used tu with his subordinates while they all used Ud. with him.
That is typical of workplace situations. One refers to his superiors as Ud., but working in the other direction is more to the discretion of the superior.
When praying, tu is used, despite the fact that it would seem to require the ultimate form of respect.
I too was surprised once to learn that tu is used to address the creator, in both Catholic and protestant/evangelical religions.
Good observations!
Hello Hyrumt and Welcome to the Spanishdict website 
The information you have learnt is correct so far as it goes but is only a general guide and is obviously not the whole picture.
tú is used with/to address family, friends/people you know well, children and people younger than you.
Ud is used to show respect to people older than you, people in authority eg your boss(es) /employer(s) and people you don't know (strangers)
•On a telenovella, a woman used tu with a man she didn't know very well to let him know that she wanted to be intimate.
This was the only one that initially surprised me after having read the first part of the sentence but having read it all I was sure this is probably correct. She is trying to indicate she is interested in getting to know him. I would imagine that the older generation over 60's and certainly over 70's would probably frown upon and dislike this practice and say the she is being much too forward and they never did it in their day P
•In a book, a chief of police used tú with his subordinates while they all used Ud. with him.
As Jeremias correctly indicates this would be normal practice within employment in places like Spain and other hispanic countries for employees to address the boss using the respectful form Ud and the boss to use tü or Ud at his discretion.
•When praying, tú is used, despite the fact that it would seem to require the ultimate form of respect.
I cannot comment on catholic tradition but I know that tú is used when addressing God in evangelical churches. I attend an English Evangelical church in England but I know/have a personal friend from Brazil who used to teach me Spanish and Portuguese who used to be our Youth Pastor and we would pray in Spanish using tú. This is not as disrepectful as it sound because:
1 In evangelical churches our faith is very bible-based and we know that being a Christian is about having a personal relationship with God through Jesus...which would require the familiar form to show relationship even though the Lord is also God Almighty. in Matthew Ch 6 v 9 in the Lord's Prayer in my Spanish Bible: La Santa Biblia Jesus says: Vosotros, pues,oraréis así (You, then ([implied should] pray in this way)
'' Padre nuestro que estás en los cielos, sanctificado sea tú nombre"'
2 The God who created us sees our heart and knows whether we are being respectful towards him or not. This is indicated not simply from our words but our heart's attiitude of love and openness towards him. I acknowledge that other people who are not Christians cannot discern this respect so easily but prayer is directed towards God and not for the purpose of impressing people or convincing them that we are being respectful to God.
•In a movie, a group of thugs used vos with a man they didn't know as a form of intimidation.
Well, this is hardly surprsing since they were trying to intimidate/frighten him They were refusing to show respect and treating him as if he were inferior in some way so they were in essence talking down to him to make him feel small!
•A father switched from tú to Ud. when he got angry with an inattentive child.
This is what I believe the father was doing and the reason/s why
In the first instance the father was emphasising relationship by using tü but moving towards a position of authority over his child and so used Ud to create distance between them both so that it became easier to discipline his child. ( i am not condoning or condemning the father's approach to discipline, here )
Spanish natives/advanced speakers : Please correct my understanding here
I hope this helps 
I asked this a while back, living in Colombia one notes that it is quite complicated to get to grip with whether to tu or not to tu.
Here are the responses generated:
My contribution, for example in spain we always use "tu" and we use "usted" when we speak with respect or with a superior, but in south america the people use "usted" and for example in Argentina they use "Vos".
Vos is use too in the old Castilian, many years ago.
Sorry for my English.
