Is it rude to ask someone for their rating before play?

I'm talking about OTB only

If you don't know someones rating when you matched up , anywhere tournament, just friends game, hustler games.

It's just makes it easier when you know someones rating just like in here on chess.com

Not at all.  Its a common practice.  I personally dont want to know, nor do i look.  

If you ask for their rating before a game, it either gives you a false sense of security if they are much lower rated than you, or if they are much higher it can only put doubts into your mind as to whether you could actually beat them. It would be best to ask at the end if the game if you do wish to know. Otherwise focus may be elsewhere, and not the game in hand.

Not exactly

I was playing this guy and he beat me twice, quite cleverly, too; I asked his rating . . . "23hundredish" . . . he says.  :(

When asked, I answer: "Ratings? What are ratings?"

These days no-one asks. They just use their smartphones to look you up in the FIDE or national database

If player is low rated, then I can play more relaxed, more agressive game, taking more risks and even taking out my quuen out early in some cases.

If my opponent high rated it's totally different game, I must play very cautious, not taking risks or experimenting as one mistake can cost a game, must be slow, position game and definitely not taking my queen out early.

So it's very important who am I playing with and what their rating is just like here online you can see straight away who you are dealing with.

I used to ask because I am extremely competitive. If someone was lower rated than me then I knew I had to beat him, and if it was someone higher rated, then the simple thought of causing an upset win over then gave me more confidence. I haven't played OTB in almost a year, but I will stop asking now when I begin playing again because it's easier to just check their ratings before playing them.