I usually get a METV. This time I will rendezvous with my fiancé in Laos, marry, and be based there.
When I booked my flight online a popup window asked if I had a visa and did I want to show it now. I declined. Will my onward ticket to Vientiane allow me to board? I am flying EVA out of the US if that matters. 

31 minutes ago, captnhoy said:

I usually get a METV. This time I will rendezvous with my fiancé in Laos, marry, and be based there.
When I booked my flight online a popup window asked if I had a visa and did I want to show it now. I declined. Will my onward ticket to Vientiane allow me to board? I am flying EVA out of the US if that matters. 

What is your nationality? Does your flight to Vientiane leave from Suvarnabhumi within a few hours after you arrive there? If doing an international to international transfer, passing Immigration in Bangkok should usually be unnecessary and you will not require a visa. (That will not be true if your flight to Vientiane leaves from Don Muang. In that case, you would need at least a transit visa or visa-on-arrival if you are not eligible for a visa exemption when entering Thailand.) If still in doubt, you should discuss your full travel itinerary with both your airlines to ensure an airside transfer is possible in your case.

1 hour ago, captnhoy said:

Will my onward ticket to Vientiane allow me to board? I am flying EVA out of the US if that matters. 

Yes. 

At departure the airline may ask for onward flight. Your ticket to Vientiane will satisfy that request.

Assume you have a USA pp.

 

Yes, I do have a USA pp. And our plan is to visit with friends in Thailand for 2 weeks or so before returning to Vientiane. Thank you both for the input.