Friendly fire vs friendly splatter?

It may just be me, but I feel like I get “accidentally” run over by my teammates a lot. Whatever, it happens. I seem to get killed more often than knocked around though. Then today, a teammate decided he wanted to run me over with his ghost, and did so. I found him afterwards and stuck his ghost with two plasmas. The ghost exploded right out from under him and he was just dandy. In another game we were losing pretty bad and it was near the end of the match. I found a teammate AFK and tried hitting him. I noticed that after two hits to the back, nothing happened. I stuck him with a plasma, nothing. Stuck again, nothing. Apparently I couldn’t kill my own teammate (not that I ever really want to!). But god almighty can they nick you with a vehicle and you’re dead. Is there a discrepancy between friendly fire from weapons and vehicles?
Or am I just imagining things?