Sometimes intentionally, but mostly unintentionally. Seen-ing is not a crime if the victim asks for it.

1 - You don’t like me, do you? 

 Maybe I did, maybe I didn’t, but mostly I didn’t pay it much attention. But now, since you frame it as a “Yes - No” question, I feel reluctant to reply because neither answer is really what I think about you. This kind of question also suggests that you have a poor image of yourself and thus makes us feel uncomfortable to continue the conversation.

2 -  Do you like spinach? I like spinach!

If you have shown any interest in the reasons why I liked spinach or not, I might have responded more enthusiastically. But when you mention that you like spinach right afterwards, it seems to me that you are only talking about yourself  and hope that my interest is similar to yours so the conversation become more convenient to you.

3 - Would your parents be sad if you die?

 If the answer to a question is almost always “Obviously, why do you ask?”, it might not be a good idea to ask it. If you have nothing to ask, it might be better to remain silent and focus on listening to your partner.

4 - I like you... 

 I cringe as I write this. Text Confession is bad. “...” makes it fucking horrendous. You might not even be able to reach the Seen-zone if you pull this shit.

5 - I’m the worst :( 

 The twin sister of You-don’t-like-me-do-you-?, only a little less uncomfortable. What do you expect us to reply? Agree with you that you really are the worst? Or is it your way of saying “Hey, pat me and say I’m the best!”

6 - :)

 Although Facebook’s latest remake of this icon seems a bit less annoying, as soon as I realize that the emoticon you use is “:)”, I immediately look at you like a cynical, fake person. Just kidding :)

7 - Hey + What are you doing? 

With or without emoticons, this combo can send you straight to the Seen-zone. You sound like a stalker who don’t even hide your intention, shamelessly invading our privacy. I myself have used this combo a few times before (mostly with caring intention), so I can assure you its effectiveness and reliability.

8 - [Holding down] (Y) 

Facebook’s slightly more polite version of “Seen”. Very effective in ending a conversation.

9 - My mom said you look a bit chubby

My female friend back in highschool threw me a disgusted look as I innocently said this to her. But it’s ok. I liked being alone anyway. Haha.

10 - haha. 

 Emoticons might not be the best way to display your emotions, but this is beyond salvation.

Source: https://www.facebook.com/notes/linh-tran/10-ideas-per-day-filler-quickest-ways-to-seen-zone/1235973089780066