Tiny, my Red Sailfin Pleco is quite the tamest and daftest pleco I've seen! I use treats for the tropicals which stick on to the side of the glass, so the fish will come and eat at the front - giving you a good chance to inspect them. Well, Tiny has now taken a liking to these treats, and is now large enough that his mouth fits around them. He will just stay there until he's eaten the whole thing.
I decided to let the other fish come and get some of the treat before Tiny polished it off, so I tapped him on the nose to get him to move. He nuzzled me back - which I thought was cute - So I tapped him again... This continued for a little while - tap...nuzzle...tap...nuzzle. Then, he decided my fingernail looked interesting, and suckered himself to that instead! I'm sure I could have lifted him out of the tank if I wanted to!
I know he wasn't attacking me by sucking on, as he lunges quite fiercely at anything which annoys him, so I can only assume this was like a display of affection. Anyone else had similar dealings?