As more Thai people enter Laos and Thai media dominates Laos, Lao language is increasingly being influenced by Thai language, and the Lao vocabulary is slowly but surely disappearing in Laos. The following are a few examples:

Fried rice

Common Lao word used in the past = "Kaow Kua"
Common Lao word used these days = "Kaow Putt"

Beautiful

Common Lao word used in the past = "Poo Ngam"
Common Lao word used these days = "Nah Huck"

Handsome

Common Lao word used in the past = "Jaow Soo"
Common Lao word used these days = "Lor" 

Lao/Thai pi nong gun

We still say "khop jai", but we tend to make Thai language the superior language when we communicate with Thais and other foreign tourists in Laos.

You're missing the point. We use their language more than they use ours.

You don't see the locals in New Zealand speak in Japanese to Japanese tourists.

Why do we have to speak in Thai all the time in our own country?

We have to blame their parents for that. If they speak Hmong to their children at home on a regular basis then that's how they learn and memorize new words and its meaning.

They'll never learn Hmong at school because everybody speaks English, so it comes down to parents and how they raise their children at home.

Lao/Thai language are very similar. Maybe some Lao want to show respected. When I was in Thai airport. They try to speak Lao to us. When they know we're from Laos

Admin Saovaluck wrote on 12^th Mar, 2012 at 6:04pm:

Thai Bangkok should understand Lao. But most Lao understand Thai and read Thai. My brother teach himself how to read Thai

Basically, it means "cute face".