Depending on the film the der der der der der der is accompanied by a 'bom bom' shortly thereafter. In the television series the sarah connor chronicles during the ending or beginning of a commercial break there is an absence of the 'bom bom' in which case a fan of the show is to tap the 'bom bom' in order to make up for the absenece of such (Im really sure they did it so that viewers would so such like, to the confusion of non terminator fans of course...).
2. When watching the original Terminator 1994 film's titles or ending. Again one is obliged to continuously tap the beat.
3. Anytime one gets the thought of the terminator one is to tap the beat.
4. The noise everyone makes in their heads when Governor Schwarzenegger is giving a public speech. (Dude thats the governator! Der der der der der der): Followed by tapping when and where possible.