they are similiar, but a little difference “突然” is a neutral phrase and always be applied in any audden situation. “唐突” is a negative phrase, when you do something offensive, it will be applied. so try not do "唐突的事" “骤然” is same to “突然”, but it usually be applied in literature works.

“突然”“骤然”相似 “唐突”带有一点冒犯别人（Offend Others）的意思，一般会在道歉（apologize）的时候说。 例句（example）：我为我的唐突向您道歉。

突然=Suddenly. adv. 唐突=brusque. adj. When you do something to others but at that time they are not that convenient, then you are 唐突。 骤然 is nearly the same as 突然, but it's more literary.

谢谢你！

什么是哪三个词的区别？----> 这三个词的区别是什么？ :)