So I hate when other people use my laptop. I don't trust other people not to mess with my stuff, and I keep my passwords saved for a bunch of websites, so I don't want people going through my email and stuff (even accidentally).

At the same time, I don't want to be a douche when a friend wants to check their email really quick, or when my dad needs to use my computer because somebody is on the other one.

Is there a program or a way I can set it up so I just click on an app or something and it just makes my personal files and saved browser stuff off-limits until I put in a password? Something quick and simple is ideal so I don't have to say "hold on" and do shit for 10 minutes before letting them use my computer. Thanks.