My latest profile is something I call "Movie Mode," though really it could be used for any DND situation.
What it does
Sets up a desktop icon that, with a press turns Movie Mode on or off. While in Movie Mode, the phone switches to vibrate and will automatically reject any incoming calls and reply to the caller with a text message saying (in my case): "[Automated Message] I'm in a movie and can't pick up right now. I'll call you back as soon as I'm out. Thanks."
If RenderFX still worked with Tasker, I'd also have it turn on the Red render, in case you need to check your phone for whatever reason and don't want to light up your whole row.
How to set it up
This one has two key elements: the first is the task that sets Movie Mode, and the other is the profile that rejects incoming calls and replies with a text message. First, the Movie Mode task. This uses the MOVTOG variable to set the state of Movie Mode (on or off) and sets silent mode accordingly.
1 If %MOVTOG = 0
2 Popup "Movie Mode ON" (optional: time 1, font size 12)
3 Silent Mode "Vibrate"
4 Variable Set %MOVTOG to 1
5 Goto Action 10
6 End If
7 Variable Set %MOVTOG to 0
8 Popup "Movie Mode OFF" (optional: time 1, font size 12)
9 Silent Mode "Off"
Then, the profile to reject incoming calls. Create a new Event-based profile with the event as "Phone -> Phone Ringing" (priority normal, number blank)
1 If %MOVTOG = 1
2 End Call
3 Send SMS (number %CNUM, message whatever you want it to be)
4 End If
And that's it! The final step is to create a Task desktop widget that points to the Movie Mode task you set up at the start. Then, whenever you press your widget, Movie Mode will turn on or off. While turned on, your phone will reject incoming calls on the first ring and send out the SMS.