Is there a singular-plural conflict in the song title "Terror Couple Kill Colonel"? [duplicate]

"Couple" can be taken as singular or plural depending on the context.

When used to refer to two people who function socially as a unit, as in a married couple, the word couple may take either a singular or a plural verb, depending on whether the members are considered individually or collectively. -The Free Dictionary

That sounds like a newspaper headline and, as such, it shows a telegraphic style of writing. In this case, in addition to what has already been mentioned by JoAnne ("couple" being considered "two persons" and verb, therefore, in the plural) the article before "terror couple" has been omitted.

Because space is limited, headlines are written in a compressed telegraphic style, using special syntactic conventions: Wikipedia

• Forms of the verb "to be" are omitted.
• Articles are usually omitted.
• Most verbs are in the simple present tense, e.g. "Governor signs bill".
• The future is expressed as "to" followed by a verb, e.g. "Governor to sign bill".
• In the US (but not the UK), conjunctions are often replaced by a comma, as in "Bush, Blair laugh off microphone mishap".
• To save space, a long word sometimes replaced by a shorter word with not quite the same meaning, e.g. "attack" to mean "criticize".

Couple is one of a couple hundred words in the English language that is categorized as collective nouns -- team is another very familiar collective noun, as are family and congregation. While it is evident these nouns describe a group -- more than one -- they do not always call for a plural verb.

With collective nouns, subject/verb agreement is determined by the manner in which the group achieves the action described by the verb: individually or collectively.

If it achieves the action collectively (as a single unit), your verb is singular:

1. The couple is awaiting arrival of its first born;
2. The team is in contention for first place;
3. The family is picnicking at Lake Luster;
4. The congregation has exceeded 350 members.

If it achieves the action by acting as individuals, your verb is plural:

1. The couple are working at opposite ends of the city;
2. The team are home with their families during the schedule hiatus;
3. The family are avid cyclists;
4. The congregation have diverse opinions on this particular church position.

In your specific example, we could assume that person one gave the guy slow-working poison on day one and person two shot him the next day. In the more likely alternative, we could assume the two people jointly beat the guy to death, and yet another song title is written in sloppy English :-)