He went in head first, not feet first, like you said. If he’d slid feet first then taken that hit, it would be obviously dirty. Lukas Van Ness catching him with an arm meant he was down, or about to be, so did he need to do it? No. In which case I’d agree, I think it was a cheapshot. It’s technically within the rules, but I think it was unnecessary and cynical.
This is actually another action that isn’t advised. Most toothpastes work (in terms of protecting your enamel) by causing a reaction between certain compounds with calcium and magnesium in them, and your saliva, to deposit them onto the enamel on your teeth, remineralising them. Rinsing your mouth with water after you’ve brushed your teeth dilutes the useful compounds in your mouth and the anti microbial agents, making it much less effective at protecting your tooth/gum health. You can just spit out the excess from brushing and go about your day.
For democracy!
If anyone is interested in knowing more about this situation, Behind the Bastards just released a 4 part series about the mentioned leader.