Looking on the internet deeply has found these results:

i'm on vacation is the most popular phrase on the web.

i'm on a vacation 1963,000 results on the web	i'm on vacation 13,960,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Don't shoot me, please. I'm on a vacation. Plus, I'm leaving on a short vacation. Princess, I'm going on a vacation soon. Well, Link, I'm going on a little vacation. I'm on a vacation. Ernie, I'm not going on a vacation. I'm on a two weeks vacation. I would love to become an Au Pair and try something new and exciting and try to be in another country a little longer than when I'm on a vacation, before I have to get an education ect.	Give me a break. I'm on vacation. Sorry, sir, I'm on vacation. Let's not talk about this stuff while I'm on vacation. I've already said I'm on vacation. Well, I'm on vacation with some friends. For me, summer is when I'm on vacation. I don't smoke except when I'm on vacation. My chief thinks I'm on vacation.

i'm on a vacation

1963,000 results on the web

i'm on vacation

13,960,000 results on the web

More popular!

Don't shoot me, please. I'm on a vacation.
Plus, I'm leaving on a short vacation.
Princess, I'm going on a vacation soon.
Well, Link, I'm going on a little vacation.
I'm on a vacation.
Ernie, I'm not going on a vacation.
I'm on a two weeks vacation.
I would love to become an Au Pair and try something new and exciting and try to be in another country a little longer than when I'm on a vacation, before I have to get an education ect.