He is clearly using it as an insult. The biggest groups of people sucking dicks are straight women and gay men. The fact he is a man saying it, and he is saying to what I assume (based ont he twitter handle) is a male troll and that somehow that's what makes it an insult is what makes it homophobic and all homophobia is an off-shoot of misogyny. There is also a power dynamic, but even in that there is a gender-role basis for determining power rather than a basis of utility. Why is the person passively getting their dick sucked the one with power? Why not the person who could stop sucking at any time or bite down? Where is the logic in determining who is dominant? It's because he is usually the man and the person sucking is usually the woman (and if you are a man sucking dick, you are seen as 'the woman', which is a negative).