Master’s and Bachelor’s

This is my favourite English mistake.

Correct use

With an ’s

A "master’s thesis" is short for "master’s degree thesis". A "master's" is the degree you do to become a master.
master’s [degree], bachelor’s [degree],
master’s [degree] thesis, bachelor’s [degree] thesis
master’s [degree] presentation


Origin of the confusion and why it's wrong

Most other languages don't include the ’s, and because the word has an English origin, they assume it's the same in English.

I can't tell you how funny I find it when people tell me "I'm doing my master". This implies you're having sex with someone who dominates over you.
"I want to do a bachelor at the University" -> You want to have sex with a single student.
"I did my master in Spain" -> You called him Maestro.

A "master thesis" would be the thesis that is the lord over all other theses.

It’s fine to say “I’m doing my M.Sc., B.Sc. or Ph. D.”.
It's also fine to say, "I'm doing my doctorate", but don't say "I'm doing my doctor" unless you are actually having sex with your doctor.