If you invade another player and when you show up in their world you see that they are engaged in a fight with a monster or NPC, do you generally hang out and let them finish the fight and heal up or do you take the opportunity to gank them while they are under duress? Personally I've always thought it polite to let them finish up what they're doing and heal up before greeting and attacking them. Sometimes the person sees me, heals up, then waves and I like to think they appreciated the breather. Other times they just attack me (for example: http://www.youtube.com/watch?v=alvvKJDaUqs).

In any case I was curious as to the community's opinion. Is letting the host finish up with a fight they're in when you invade good etiquette or is it just a failure to strike at the most opportune moment?