Regret

When i was pursuing my MBA ,in semester practicals,
1St incident
There was a spoken English class . in the class teacher asked me why i was absent last three days . ( i was weak in english ) i said that i had a "MUSCLE FRACTURE ".
The whole class laughed at me ,then  laughingly teacher told be muscles can't be fractured, it shuold be muscle pull .

2nd incident
 faculty gave me the topic " rasism " for presentation .
I presented it at front of a guest faculty.
I confuced the words cast differenciation and casting cauch as the same startings .
I thought that they are the same . i never knew that the word " casting couch is belongs to a really degraded thing which people use to force someone to do 'work' what they never want to do. When the guest talked about the rasism, she gave me some hints that i was at a mistake .

Than i realized it  and i solved my mistakes.
But i regret that why i never got the skills of spoken english , why it is too hard to get , why i stammer when i give a presentation or an interview.it can be a humorous incident for anyone ,but i felt shamefull most of the time when i face this type of situations.
WHY ,WHY ,WHY