Whenever I used an underscore it automatically adds those curly brackets to it. Now sometimes thats nice, but sometimes you really dont need this. Is there a way to disable that feature? I roamed through the options several times now but can't find the one regarding my problem.
There are two ways you can control this behaviour in TeXShop: permanently or temporarily.
At the top of each source window there should be a check box called Key Bindings. (If it's not there, you can add it by choosing the Customize Toolbar item from the Window Menu and dragging it to the toolbar.)
If you unclick the checkbox, you can turn off all automatic substitutions temporarily.
If you want to change just the behaviour of the underscore or caret, you can permanently change them by choosing the Key Bindings menu item from the Source menu. This will give you the Key Bindings editor and you can change any key binding you like:
Can't you simply use a backslash?