1) How did you know if I repeated myself a bunch when you didn't read my posts?
2) For your first point, I was talking about teabagging in general, which seabagging was based off of. Teabagging represents a... sexual act forced upon, video game animation or not; they wouldn't be doing it anyway. The middle finger represents a... thing, like you said, being... well, you know, but it's got a similar intention; representing a sexual act.
And how do you know that's how teabagging originated in video games? I looked it up just now and didn't see anything backing up what you said, but I found it commonly called things akin to "the ultimate sign of disrespect", and because people were far away and ambiguous and not next to you at an arcade, they could get away with it. Keep in mind that a source that referred to the act as disrespectful agreed that the bobbing up and down animation looked funny. It started off in Halo, then earned its name in the second iteration and became more common due to the camera lingering for a while over corpses. The act is commonly frowned upon by older gamers, who usually report or kick players doing that kind of thing, and when a COD game rewarded players for teabagging, reviewers weren't really happy with it. As gamers mature, they tend to usually find the act immature and childish. That's what I found, and it looks like you're fighting an army of conflicting opinions on the matter when it comes to said gamers.
So yes, there is at least some comparison, if not to the point I showed.
Now, to your comment about how we can't determine how teabagging is intended: You're right; we can't determine it, and there are some like you who do it out of joking around. But the act of teabagging is obviously interpreted by plenty as disrespectful, and if others wanted to send the message of, "Come and get me! Hahaha!" why not just jump around while on screen in celebration or something instead of looking like you're trying to make a corpse "suck"? It's not hard.
People will be at least a little suspicious of trollish activity, even if they ignore it, and it's okay, especially considering the act's roots. It's a video game? Yes, but that changes nothing, because it's still taking advantage of being anonymous over the internet. We can be at least a little suspicious of whether or not there MAY be a troll trying to pester people, even if we ignore it and brush it off. This is my mindset when I play: If someone seabags me, I'll ignore it, but I will wonder how they are as people unless I know them. We don't know for sure if the person doing it now is one, but there has to be plenty among the group that has done so. Can't be overly sensitive about that.