In 'Sex Tape', Diaz and Jason Segel play a couple who used to have sex 24/7 (the opening few minutes is just them bragging about that) but now married life and children get in the way of that. During a night without the kids, they decide to film themselves having sex. A little later, Segel receives a text complimenting him on the video. Segel then realises that the video has accidentally been synced/sent to various iPads they'd given to friends. The bit where he is struck with the horror of this was probably the only moment I found to be remotely amusing in the whole film.
Anyway, after that the couple decide they need to go around to the various locations of the iPads (*cough*product placement*cough*) they gave out and delete the video from each one, leading to them doing stupid things that, I think, are meant to be funny but more just signify that this film has no idea what to do or how to do it that it just throws whatever it can at you and hopes it'll work. This is especially evident when the film isn't over after the iPads have been dealt with. Instead, more stuff has to apparently be dealt with, leading to bits that are even more unfunny than before.
'Sex Tape' probably thinks its central premise is genius but all this leads to is an unfunny 'comedy' bereft of any ideas resulting in some sloppy, forced shamble.