Being too honest or you can say... being too frank

Especially, don't know what's wrong with me...I was being too frank to 2person who I'm not close with.. in a not very good way...

1st incident:..
I talked down that Lecturer who my group was presenting to..: He interrupted us half-way in every slides and ask questions+give us "suggestions" about how to make it better(or can I say that he say our slides are no good). It's like I have just started presenting my 1st slide not long ago, and I haven't even complete my first sentense of the objective of that project, He cut in and talk AGAIN~Fine, I listen!
After that I discovered that he repeated what said earlier on, I'm so frustrated seriously.
Him:"Skip this slide"
and we played the video in the next slide...
Him:*Asking questions on what this project is about, and why we didn't explain what this project is about...and ask ask ask!*
Me:*WOW WHO JUST TOLD US TO SKIP THAT SLIDE(regarding what that project is about?!!!)*
Me: "We have a slide that we've prepared to explain about that, but you say you don't want see just now, so can I explain on that NOW?"
*At this moment, I really don't get why the other lecturers and group members were laughing(silent laughters)*
Him: *Stunned* , "Alright explain now"

However after the whole presentation, then I realised... I was being way too frank(in a sense that it might appear to be rude to him)... I can see that he's kindda mind about me being like that..and I guess he got angry.<-I will guess about that because he went into our project room suddenly, and told me about "You guys should place a siren beside the sensor.... ....rude"<-He did says something about being rude but I didn't catch it that time. and his face don't look right...(or don't look happy)
Hopefully he didn't give us a 'D' grade for our presentation... lol I want at least a 'B'

2nd incident is....: This friend from other project group came and chatted with us...We all ended up telling him to sing the song that he says he can imitate that singer singing's voice which will sounds like that singer. He sang and I was very amazed and feel that he really sounds like that singer.
I have no ideas what did we talked which led me saying him "But your singing pronuncation not accurate"..."Neither do I have perfect chinese pronuncation but I'm just saying"
And DDANG, Him:"Ya la, then you still say~!You also cannot still comment like that!"
Can see that I'm kindda offended him in some way....

I suppose I shouldn't talk without filtering off some very frank thoughts...
In a day, I have offended and hurt 2 person. Maybe I should just think twice before talking.
It's my fault~
My day today wasn't very good to start off with already...