While some people might like to ‘suck it,’ it’s usually with people they know and like. If I tell somebody to ‘suck it’ it usually means that I don’t like them, and they don’t like me (or I’m just begging). I’m expressing my disdain for them by telling them to do something they’d probably find gross.
On a side note, telling people to suck things as an insult doesn’t always work. I got into an arguement with a cute girl at a party once, and she eventually got really pissed and said ‘suck my tit.’ I was pretty dissapointed when I found out she was bluffing.