Re:   "Suck it up"   

Double:

   It means that one should shut up,  forget about complaining, and endure discomfort or pain.

Is it "fashionable"?   Sure it is fashionable.  All you have to do is be willing to offend everyone you speak to,  become a social pariah,  and look like a person who is offensive in the worst way to nearly everyone.

 Seriously.  Many foreign students  are oblivious to the fact that Native Speakers of English,  such as Americans, will use offensive expressions   toward other people to express hostility or contempt.

  Americans can be seen, in many of their Idioms and Slang Expressions, to be willing to offend just about anyone.  Americans in their speech can be highly aggressive. That is why it is so risky for Foreign Students of English to try to adopt  Slang  communications  in an attempt to "Fit In"  with the "locals".  

   Using a phrasing like  "Suck It Up!" in some social situation is liable to get your face slapped or worse by a very angry  American who does not appreciate the appearance of being dominated in any social setting by another.

  Amongst close friends,   such expressions,  inclusive of profanity or other insulting language  is understood as entertainment.  However, you can never be entirely certain that some person is not going to have a negative reaction to you.

      Children in the schoolyard in America will say things like;  "Suck it up,Fatty!"  and they fully intend to express their willingness to engage in violence with anyone who disagrees with the expression.

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"suck it up" meaning is to accepting something unpleasant and get over it and move along

This is a pretty common expression in Australia. Other equivalents would be to say to someone, "harden up/toughen up". It's like telling a person to stop whinging or complaining and to just just deal with things.

It's also pretty common to in Australia to say "suck it up, princess", if you really want to belittle someone.

It's fairly fashionable among guys who like to think they're prettty tough but it isn't too offensive to say to someone where I'm from, however Australians are known to be a pretty unrefined bunch and a little politically incorrect.

It's not really used in the UK. I think others have done well at explaining it. I'd just like to add that you would really only use it with people you know well and if they were complaining about something relatively minor. Obviously saying it to someone who has real problems is very rude and unhelpful.

Jacky, I'm afraid that you are wrong. "Suck it up" is not a swearing phase at all. It's "sucks"