Being too busy.

Whichever types of busy that is, if he/she are too busy to even text you then, you are preeeeetttty low on their priority list. (relationship in general, friends, family etc) Considering it doesn't take even a few seconds to write a text reply.

I think you are looking at it wrong. It doesn't really matter what they are doing if they said they busy then don't stress out about it. If you have the feeling that they are avoiding you let time pass and if this is a repeating thing then they are most likely not interested. I agree with Haruu 100% I've heard women use that line before.