It seems that if you press TAB and type "say messageyouwanttosay" or press T and directly type your message in-game, you will say something and a MoonBase Alpha voice will read your message.

Well, if you have played MoonBase Alpha you will know what to do >:D
But if you haven't played that wonderful game I can link some guides you will surely follow, in order to laugh like a stupid (or, at least, make a smile)

http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=125735997&searchtext=how+to+aeiou

http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=128648903

So don't be shy, copy-paste those strings or create some new ones, and have fun :)