Someone who hangs around when they are usually unwanted and is only interested in what they can get out of people. They are generally annoying and often ruin what would otherwise be perfectly nice days out.
“Ugh, now I have to share my chips with her because she swooped in just as I bought them, she’s such a gannet."
Used to describe someone who is just an absolute good for nothing clown. Can also be used as 'Gannetacious' as in; look at that person doing something stupid, yeah hard that's gannetacious of them.