ATTENTION; South African Passport Holders
Sorry to be the bearer of bad news but;
IF you entered thailand on a tourist visa from the thai consulate in Pretoria and it has any thai writing on the visa itself you CANNOT go to Vientiane and get a visa. :/
IF you have a visa from the consulate in Pretoria and it has NO Thai writing on it OR you came into the country on a 30 day visa exempt entry stamp you're fine to go to Vientiane for a visa. It's only visas from the thai consulate in Pretoria that have thai writing on them. :(
This is an example of what it looks like;